Review: passive immunity in beef-suckler calves.

Colostrum-derived passive immunity is central to the health, performance and welfare of neonatal beef-suckler calves, and economics of beef-farming enterprises. Compared to dairy calves, mainly Holstein-Friesian, there is much less research carried out on passive immunity and associated factors in beef calves. Thus, this review aimed to summarise and interpret published information and highlight areas requiring further research. The transfer of immunoglobulin G1 (IgG1) from blood to mammary secretions is greater for beef × dairy cows compared to most beef breed types. Considerable between-animal variance is evident in first-milking colostrum yield and immunoglobulin concentration of beef-suckler cow breed types. First-milking colostrum immunoglobulin concentrations are similar for within-quarter fractions and for the front and rear quarters of the udder. First-milking colostrum yield is higher for beef × dairy cows than beef × beef and purebred beef breeds, and higher for multiparous than primiparous cows, but generally colostrum immunoglobulin concentration is relatively similar for each of the respective categories. Consequently, colostrum immunoglobulin mass (volume × concentration) production in beef cows seems to be primarily limited by colostrum volume. The effect of maternal nutrition during late gestation on colostrum yield is not well documented; however, most studies provide evidence that colostrum immunoglobulin concentration is not adversely affected by under-nutrition. Factors that impinge upon the duration between birth and first suckling, including dam parity, udder and teat anatomy and especially dystocia, negatively impact on calf passive immunity. Colostrum immunoglobulin mass ingested relative to birth weight post-parturition is the most important variable determining calf passive immunity. Research indicates that feeding the beef calf a colostrum volume equivalent to 5% of birth weight shortly after parturition, with subsequent suckling of the dam (or a second feed) 6 to 8 h later, ensures adequate passive immunity, equivalent to a well-managed suckling situation. Within beef-suckler cow genotypes, calf passive immunity is similar for many common beef breeds, but is generally higher for calves from beef × dairy cows. Compared to older cows, calves from younger cows, especially primiparous animals, have lower serum immunoglobulin concentrations. Most studies have shown no adverse impact of maternal dietary restriction on calf passive immunity. The prevalence of failure of passive transfer (FPT) in beef calves varies considerably across studies depending on the test used, and what cut-off value is assumed or how it is classified. The accuracy and precision of methodologies used to determine immunoglobulin concentrations is concerning; caution is required in interpreting laboratory results regarding defining colostrum 'quality' and calf passive immune 'status'. Further research is warranted on colostrum-related factors limiting passive immunity of beef calves, and on the validation of laboratory test cut-off points for determining FPT, based on their relationships with key health and performance measures.

An observational study on passive immunity in Irish suckler beef and dairy calves: Tests for failure of passive transfer of immunity and associations with health and performance.

The study objectives were to: 1) evaluate the diagnostic performance of passive immunity tests for classification of failure of passive transfer (FPT) risk, based on their relationships with calf health and performance, and 2) describe the epidemiology of morbidity and mortality in suckler beef and dairy calves under Irish conditions. A total of 1392 suckler beef calves (n = 111 farms) and 2090 dairy calves (84 farms) were included in this observational study. Blood samples were collected by jugular venipuncture. Serum samples were analysed for total IgG concentration using an ELISA assay, total protein concentration by clinical analyser (TP - CA), globulin concentration, zinc sulphate turbidity (ZST) units, total solids percentage by Brix refractometer (TS - BRIX), and total protein concentration by digital refractometer (TP - DR). Crude and cause-specific morbidity, all-cause mortality, and standardised 205-day body weight (BW) were determined. Generalised linear mixed models were used to evaluate associations between suckler beef and dairy calves for morbidity, mortality, growth and passive immunity. Receiver operating characteristic (ROC) curves were constructed to determine optimal test cut-offs for classification of health and growth outcomes. Overall, 20% of suckler beef and 30% of dairy calves were treated for at least one disease event by 6 mo. of age. Suckler beef calves had greater odds of bovine respiratory disease (BRD; odds ratio (OR), 95% confidence interval (CI): 2.8, 1.2-6.5, P = 0.01), navel infection (5.1, 1.9-13.2, P < 0.001), and joint infection/lameness (3.2, 1.3-7.8, P = 0.01) during the first 6 mo. of life than dairy calves. In addition, from birth to 6 mo. of age, suckler beef calves had greater rates of navel infection (incidence rate ratio (IRR), 95% CI: 3.3, 1.3-8.4, P = 0.01), but decreased rates of diarrhoea (0.9, 0.2-0.9, P = 0.03) compared to dairy calves. Optimal test cut-offs for classification of morbidity and mortality outcomes in suckler beef calves ranged from 8 to 9 mg/ml ELISA, 56 to 61 g/l TP - CA, 26 to 40 g/l globulin, 12 to 18 ZST units, 8.4% TS - BRIX, and 5.3 to 6.3 g/dl TP - DR. Optimal test cut-offs for classification of morbidity and growth outcomes in dairy calves ranged from 10 to 12 mg/ml ELISA, 57 to 60 g/l TP - CA, 29 to 34 g/l globulin, 19 ZST units, 7.8 to 8.4% TS - BRIX, and 5.7 to 5.9 g/dl TP - DR.

Blood immune transcriptome analysis of artificially fed dairy calves and naturally suckled beef calves from birth to 7 days of age.

Neonatal calves possess a very immature and naïve immune system and are reliant on the intake of maternal colostrum for passive transfer of immunoglobulins. Variation in colostrum management of beef and dairy calves is thought to affect early immune development. Therefore, the objective of this study was to examine changes in gene expression and investigate molecular pathways involved in the immune-competence development of neonatal Holstein dairy calves and naturally suckled beef calves using next generation RNA-sequencing during the first week of life. Jugular whole blood samples were collected from Holstein (H) dairy calves (n = 8) artificially fed 5% B.W. colostrum, and from beef calves which were the progenies of Charolais-Limousin (CL; n = 7) and Limousin-Friesian beef suckler cows (LF; n = 7), for subsequent RNA isolation. In dairy calves, there was a surge in pro-inflammatory cytokine gene expression possibly due to the stress of separation from the dam. LF calves exhibited early signs of humoral immune development with observed increases in the expression genes coding for Ig receptors, which was not evident in the other breeds by 7 days of age. Immune and health related DEGs identified as upregulated in beef calves are prospective contender genes for the classification of biomarkers for immune-competence development, and will contribute towards a greater understanding of the development of an immune response in neonatal calves.

Stress and immunological response of heifers divergently ranked for residual feed intake following an adrenocorticotropic hormone challenge.

BACKGROUND: When an animal is exposed to a stressor, metabolic rate, energy consumption and utilisation increase primarily through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Changes to partitioning of energy by an animal are likely to influence the efficiency with which it is utilised. Therefore, this study aimed to determine the physiological stress response to an exogenous adrenocorticotropic hormone (ACTH) challenge in beef heifers divergently ranked on phenotypic residual feed intake (RFI). RESULTS: Data were collected on 34 Simmental weaning beef heifers the progeny of a well characterized and divergently bred RFI suckler beef herd. Residual feed intake was determined on each animal during the post-weaning stage over a 91-day feed intake measurement period during which they were individually offered adlibitum grass silage and 2 kg of concentrate per head once daily. The 12 highest [0.34 kg DM/d] and 12 lowest [-0.48 kg DM/d] ranking animals on RFI were selected for use in this study. For the physiological stress challenge heifers (mean age 605 ± 13 d; mean BW 518 ± 31.4 kg) were fitted aseptically with indwelling jugular catheters to facilitate intensive blood collection. The response of the adrenal cortex to a standardised dose of ACTH (1.98 IU/kg metabolic BW0.75) was examined. Serial blood samples were analysed for plasma cortisol, ACTH and haematology variables. Heifers differing in RFI did not differ (P = 0.59) in ACTH concentrations. Concentration of ACTH peaked (P < 0.001) in both RFI groups at 20 min post-ACTH administration, following which concentration declined to baseline levels by 150 min. Similarly, cortisol systemic profile peaked at 60 min and concentrations remained continuously elevated for 150 min. A RFI × time interaction was detected for cortisol concentrations (P = 0.06) with high RFI heifers had a greater cortisol response than Low RFI from 40 min to 150 min relative to ACTH administration. Cortisol response was positively associated with RFI status (r = 0.32; P < 0.01). No effect of RFI was evident for neutrophil, lymphocytes, monocyte, eosinophils and basophil count. Plasma red blood cell number (6.07 vs. 6.23; P = 0.02) and hematocrit percentage (23.2 vs. 24.5; P = 0.02) were greater for low than high RFI animals. CONCLUSIONS: Evidence is provided that feed efficiency is associated with HPA axis function and susceptibility to stress, and responsiveness of the HPA axis is likely to contribute to appreciable variation in the efficiency feed utilisation of cattle.

Effect of space allowance and floor type on performance, welfare and physiological measurements of finishing beef heifers.

Accommodating cattle indoors during the winter is widely practiced throughout Europe. There is currently no legislation surrounding the space allowance and floor type that should be provided to cattle during this time, however, concerns have been raised regarding the type of housing systems currently in use. The objective of the study was to investigate the effect of space allowance and floor type on performance and welfare of finishing beef heifers. Continental crossbred heifers (n=240: mean initial live; weight, 504 (SD 35.8) kg) were blocked by breed, weight and age and randomly assigned to one of four treatments; (i) 3.0 m2, (ii) 4.5 m2 and (iii) 6.0 m2 space allowance per animal on a fully slatted concrete floor and (iv) 6.0 m2 space allowance per animal on a straw-bedded floor, for 105 days. Heifers were offered a total mixed ration ad libitum. Dry matter intake was recorded on a pen basis and refusals were weighed back twice weekly. Heifers were weighed, dirt scored and blood sampled every 3 weeks. Whole blood was analysed for complete cell counts and serum samples were assayed for metabolite concentrations. Behaviour was recorded continuously using IR cameras from days 70 to 87. Heifers' hooves were inspected for lesions at the start of the study and again after slaughter. Post-slaughter, carcass weight, conformation and fat scores and hide weight were recorded. Heifers housed at 4.5 m2 had a greater average daily live weight gain (ADG) than those on both of the other concrete slat treatments; however, space allowance had no effect on carcass weight. Heifers accommodated on straw had a greater ADG (0.15 kg) (P<0.05), hide weight (P<0.01) better feed conversion ratio (P<0.05) and had greater dirt scores (P<0.05) at slaughter than heifers accommodated on concrete slats at 6.0 m2. The number of heifers lying at any one time was greater (P<0.001) on straw than on concrete slats. Space allowance and floor type had no effect on the number of hoof lesions gained or on any of the haematological or metabolic variables measured. It was concluded that increasing space allowance above 3.0 m2/animal on concrete slats was of no benefit to animal performance but it did improve animal cleanliness. Housing heifers on straw instead of concrete slats improved ADG and increased lying time; however carcass weight was not affected.

Invited review: Relationship between cattle transport, immunity and respiratory disease.

The association between transportation and the occurrence of the bovine respiratory disease complex (BRDC) has long been recognised. Many hypotheses regarding this association have been declared through the past decades, and it is agreed upon by most researchers that the multiple stressors that calves experience during transportation result in an overall immunosuppression that allows the respiratory tract to be invaded by numerous opportunistic pathogens. Furthermore, the innate immune cells, neutrophils, may be trapped in a paradox whereby their crucial defence and pathogen-killing activities are counteracted by excessive inflammation and tissue damage that may exacerbate disease, including the BRDC. Neutrophilia in response to glucocorticoids has been attributed to an influx of immature neutrophils newly released from the bone marrow, a decrease in neutrophil margination along endothelial walls, and a decrease in neutrophil apoptosis. Several of these explanations have been confirmed by altered expression of genes and proteins important for neutrophil margination and apoptosis.

Evaluation of factors associated with immunoglobulin G, fat, protein, and lactose concentrations in bovine colostrum and colostrum management practices in grassland-based dairy systems in Northern Ireland.

The objectives of this study were to investigate colostrum feeding practices and colostrum quality on commercial grassland-based dairy farms, and to identify factors associated with colostrum quality that could help inform the development of colostrum management protocols. Over 1 yr, background information associated with dairy calvings and colostrum management practices were recorded on 21 commercial dairy farms. Colostrum samples (n = 1,239) were analyzed for fat, protein, lactose, and IgG concentration. A subset was analyzed for somatic cell count and total viable bacteria count. Factors associated with nutritional and IgG concentrations were determined using both univariate and multivariate models. This study found that 51% of calves were administered their first feed of colostrum via esophageal tube, and the majority of calves (80%) were fed >2 L of colostrum at their first feed (mean = 2.9 L, SD = 0.79), at a mean time of 3.2 h (SD 4.36) after birth, but this ranged across farms. The mean colostral fat, protein, and lactose percentages and IgG concentrations were 6.4%, 14%, 2.7%, and 55 mg/mL, respectively. The mean somatic cell count and total viable count were 6.3 log10 and 6.1 log10, respectively. Overall, 44% of colostrum samples contained <50 mg/mL IgG, and almost 81% were in excess of industry guidelines (<100,000 cfu/mL) for bacterial contamination. In the multivariate model, IgG concentration was associated with parity and time from parturition to colostrum collection. The nutritional properties of colostrum were associated with parity, prepartum vaccination, season of calving, and dry cow nutrition. The large variation in colostrum quality found in the current study highlights the importance of routine colostrum testing, and now that factors associated with lower-quality colostrum on grassland-based dairy farms have been identified, producers and advisers are better informed and able to develop risk-based colostrum management protocols.

Effect of concentrate supplementation during the dry period on colostrum quality and effect of colostrum feeding regimen on passive transfer of immunity, calf health, and performance.

The objectives were to evaluate the effect of (1) supplementing concentrates to multiparous Holstein cows during the dry period on colostral and milk immunoglobulin G (IgG) concentration; and (2) feeding calves colostrum at either 5 or 10% of their body weight (BW) on passive transfer of immunity, health, and performance. Holstein multiparous cows (n=37) were assigned to 1 of 2 nutritional treatments during an 8-wk dry period: (1) offered ad libitum grass silage only (GS) or (2) offered ad libitum access to the same grass silage plus concentrate [total mixed ration in a 75:25 dry matter (DM) ratio], providing a mean concentrate DM intake of 3.0kg/cow per day (GSC). Both treatment groups were offered identical levels of mineral and vitamin supplementation. Calves from these cows were weighed immediately after birth and fed either 5% (5BW) or 10% (10BW) of their BW in colostrum from their own dams within 2.5h of birth. Calves in the 10BW group received their second feed of colostrum from first-milking colostrum. Concentrate supplementation during the dry period had no effect on colostral IgG concentration, first-milking IgG yield, or fat, protein, and lactose contents. However, cows in GSC produced a greater mean milk yield over the first 8 milkings compared with cows in the GS group. Concentrate supplementation had no effect on calf BW or BW gain, serum IgG, or apparent efficiency of absorption (AEA) at 24h after birth. However, offspring from the GSC group had fewer cases of enteritis during the first 56d of life compared with offspring from the GS group. Calves in the 10BW group had greater mean serum IgG concentration for the first 3d following birth; however, at 24h after birth, we observed no treatment effect on AEA. The rate of enteritis was greater for calves in the 5BW treatment compared with 10BW. The colostrum-feeding regimen had no effect on BW gain or on the incidence of pneumonia among calf treatment groups. In conclusion, concentrate supplementation regimens offered during the dry period had a positive effect on colostrum yield, and offspring from the GSC group had a reduced rate of enteritis. Feeding 10% of BW of colostrum versus 5% of BW resulted in a greater serum IgG concentration for the first 3d postpartum, and 10BW calves had a reduced rate of enteritis. Overall, to achieve successful passive transfer, decrease the rate of enteritis, and increase efficiency in the dairy calf, we recommend that dairy calves be fed 10% of their BW in colostrum as soon as possible after birth.

A retrospective epidemiological analysis of risk factors for a primary necropsy diagnosis of bovine respiratory disease.

Bovine respiratory disease (BRD) is a multifactorial disease and the primary cause of both bovine morbidity and mortality in Ireland. The risk factors associated with a primary necropsy diagnosis of BRD among cattle in the traditional (non-feedlot) husbandry systems prevalent in Ireland have not been investigated previously. The aim of this case-control study was to investigate those risk factors among cattle of all ages over an 8 year period. A total of 3,090 BRD cases and 5,236 controls were matched by submitting veterinary practitioner. Univariable and multivariable analyses were performed to examine the association of selected animallevel, herd-level and environmental risk factors with case or control status using a conditional logistical regression model. Male cattle aged more than 31 days were significantly more likely to record a primary necropsy diagnosis of BRD than female cattle. Older cattle of both sexes were at increased odds of a BRD necropsy diagnosis than younger calves with the exception of female cattle aged greater than 165 days. The risk of a primary necropsy diagnosis of BRD increased with increasing herd size and decreased with increasing time in days since the last animal movement into the submitting herd. There were significantly reduced odds of a primary necropsy diagnosis of BRD in the summer (June to August) when compared with the autumn (September to November). These findings identify significant risk factors for a necropsy diagnosis of BRD under non-feedlot-type husbandry conditions.

Characterisation of the Whole Blood mRNA Transcriptome in Holstein-Friesian and Jersey Calves in Response to Gradual Weaning.

Weaning of dairy calves is an early life husbandry management practice which involves the changeover from a liquid to a solid feed based diet. The objectives of the study were to use RNA-seq technology to examine the effect of (i) breed and (ii) gradual weaning, on the whole blood mRNA transcriptome of artificially reared Holstein-Friesian and Jersey calves. The calves were gradually weaned over 14 days (day (d) -13 to d 0) and mRNA transcription was examined one day before gradual weaning was initiated (d -14), one day after weaning (d 1), and 8 days after weaning (d 8). On d -14, 550 genes were differentially expressed between Holstein-Friesian and Jersey calves, while there were 490 differentially expressed genes (DEG) identified on d 1, and 411 DEG detected eight days after weaning (P < 0.05; FDR < 0.1). No genes were differentially expressed within breed, in response to gradual weaning (P > 0.05). The pathways, gene ontology terms, and biological functions consistently over-represented among the DEG between Holstein-Friesian and Jersey were associated with the immune response and immune cell signalling, specifically chemotaxis. Decreased transcription of several cytokines, chemokines, immunoglobulin-like genes, phagocytosis-promoting receptors and g-protein coupled receptors suggests decreased monocyte, natural killer cell, and T lymphocyte, chemotaxis and activation in Jersey compared to Holstein-Friesian calves. Knowledge of breed-specific immune responses could facilitate health management practices better tailored towards specific disease sensitivities of Holstein-Friesian and Jersey calves. Gradual weaning did not compromise the welfare of artificially-reared dairy calves, evidenced by the lack of alterations in the expression of any genes in response to gradual weaning.

Endocrine and hematological responses of beef heifers divergently ranked for residual feed intake following a bovine corticotropin-releasing hormone challenge.

The objective of this study was to determine if beef heifers divergently ranked on phenotypic residual feed intake (RFI) differed in their physiological stress response to an exogenous bovine corticotropin-releasing hormone (bCRH) challenge. Yearling Limousin × Friesian heifers ( = 86) were ranked by RFI. The 15 highest (mean 0.66 kg DM/d; high RFI) and 15 lowest (mean -0.72 kg DM/d; low RFI) ranking animals were used for this study. During the study period, heifers (mean age 485 ± 13 d; mean BW 408 ± 31.4 kg) were housed in a slatted-floor facility. To facilitate intensive blood collection, heifers were fitted aseptically with indwelling jugular catheters. All heifers received dexamethasone (DEX; 20 µg/kg BW i.m.) 12 h before the bCRH challenge (d 0). Heparinized blood samples were collected at -60 and 0 min before administration of DEX, and 12 h after DEX administration. Following DEX administration, cortisol and dehydroepiandrosterone (DHEA) concentrations similarly decreased ( ≥ 0.22) between high and low RFI groups. The response of the HPA axis to a standardized dose of bCRH (0.3 µg/kg BW) was examined. On d 0, serial blood samples were collected at -20, 0, 20, 40, 60, 80, 100, 120, 150, 180, 210, 240, 270, 330, and 390 min relative to the time of bCRH administration (0 min) and were analyzed for plasma cortisol and DHEA concentrations. Blood hematology variables were also determined at -20, 0, 20, 80, 150, 270, 330, and 390 min relative to bCRH administration. Neither an RFI × sampling time interaction nor a direct effect of RFI were detected ( ≥ 0.36) for plasma cortisol, DHEA concentrations, or cortisol:DHEA ratio. An effect of sample time was observed for cortisol ( < 0.001), DHEA ( = 0.04), and cortisol:DHEA ( = 0.02), with cortisol concentration peaking at 60 min post-CRH administration. The maximum concentration and rate of change in cortisol and DHEA concentrations following bCRH administration were not different ( ≥ 0.20) between the high and low RFI phenotypes. Similarly, an effect of RFI was not evident ( ≥ 0.16) for any of the hematology variables examined including neutrophil, lymphocyte, and leukocytes counts; white and red blood cell numbers; and hemoglobin concentrations. Our results suggest that responsiveness of the HPA to stress, at least at the level of the anterior pituitary gland, is not a significant contributor to variation in RFI among growing beef heifers.

Fertility and genomics: comparison of gene expression in contrasting reproductive tissues of female cattle.

To compare gene expression among bovine tissues, large bovine RNA-seq datasets were used, comprising 280 samples from 10 different bovine tissues (uterine endometrium, granulosa cells, theca cells, cervix, embryos, leucocytes, liver, hypothalamus, pituitary, muscle) and generating 260 Gbases of data. Twin approaches were used: an information-theoretic analysis of the existing annotated transcriptome to identify the most tissue-specific genes and a de-novo transcriptome annotation to evaluate general features of the transcription landscape. Expression was detected for 97% of the Ensembl transcriptome with at least one read in one sample and between 28% and 66% at a level of 10 tags per million (TPM) or greater in individual tissues. Over 95% of genes exhibited some level of tissue-specific gene expression. This was mostly due to different levels of expression in different tissues rather than exclusive expression in a single tissue. Less than 1% of annotated genes exhibited a highly restricted tissue-specific expression profile and approximately 2% exhibited classic housekeeping profiles. In conclusion, it is the combined effects of the variable expression of large numbers of genes (73%-93% of the genome) and the specific expression of a small number of genes (<1% of the transcriptome) that contribute to determining the outcome of the function of individual tissues.

Characterisation of haematological profiles and whole blood relative gene expression levels in Holstein-Friesian and Jersey bull calves undergoing gradual weaning.

Haematological profiles indicate the health status of an animal and can be used to identify sub-clinical stress responses. The objectives of the study were to examine (i) the effect of breed and plane of nutrition, on haematological profiles of artificially reared Holstein-Friesian and Jersey bull calves in response to gradual weaning, and (ii) the effect of breed on immune response genes in bovine whole blood using real-time quantitative PCR. Holstein-Friesian and Jersey bull calves were group housed indoors and individually fed using an automatic feeder. They were allocated to a high, medium or low plane of nutrition, based on milk replacer (MR) and concentrate. The nutrition treatments were calculated using National Research Council guidelines in order to achieve a high, medium or low growth rate for each respective breed. During the weaning phase MR was gradually reduced over a 14-day (d) period (d -13 to d 0). Calves were blood sampled on d -14, -6, -3, 0, 1, 3, 8 and 14 relative to weaning (d 0) for subsequent haematological analysis. On d -14, 1 and 8, a subset of eight Holstein-Friesian calves randomly selected from the medium nutrition treatment and eight Jersey calves randomly selected from the high nutrition treatment, were blood sampled for gene expression profiling, targeting biomarkers of weaning stress. These two treatment groups were chosen to examine the effect of breed on expression of the genes of interest, as energy intake and animal performance were similar. There was no effect of breed×plane of nutrition interaction nor effect of plane of nutrition on any variable measured (P>0.05). Gradual weaning produced differential biological responses in the two breeds evidenced by breed×time interactions for lymphocyte, monocyte and red blood cell number, plasma haemoglobin and haptoglobin concentrations (P<0.05). The typical stress response consisting of neutrophilia and lymphopaenia was not observed for any treatment. An immune response to gradual weaning was observed as the relative gene expression level of the pro-apoptotic gene, Fas, increased on d 1 relative to d -14 (P<0.05). Relative gene expression levels were greater in Jersey calves compared with Holstein-Friesian for the pro-inflammatory cytokine CXCL8 (P=0.05) and the glucocorticoid receptor, GRα (P<0.05). The increased levels of these transcripts suggest that Jersey calves may have a more sensitive immune system compared with Holstein-Friesian.

Controlling nematodes in dairy calves using targeted selective treatments.

With increasing concerns of anthelmintic resistance in cattle nematode populations worldwide, there is a need to explore alternative approaches to nematode control. One alternative approach is the use of targeted selective treatments (TST) where only individual animals are treated instead of the entire group. This study reports the findings of a TST approach in dairy calves conducted over their first grazing season (FGS) to control both gastrointestinal nematode and lungworm challenge. Ninety-six calves with an initial mean (s.d.) age and live weight of 130 (28.3) days and 120 (23.6)kg, respectively, were randomised by breed, age and live weight to one of two treatments; Control (n=24; ×2) and TST (n=24; ×2). Control calves were treated three times at pasture with ivermectin by subcutaneous injection. Individual calves in the TST group were treated at pasture with ivermectin when one of the following thresholds was met: (1) positive for lungworm larvae using the modified Baermann technique or (2) positive or negative for lungworm larvae using the modified Baermann technique with plasma pepsinogen concentration (PP) ≥ two international units of tyrosine/litre and faecal egg count (FEC) ≥ 200 strongyle eggs per gram of faeces. Calves were rotationally grazed from July 3rd 2012 (day 0) to November 2nd 2012 (day 122) when calves were housed. Calves were weighed and sampled (blood and faecal) every three weeks. There was an effect of treatment and time on both FEC [treatment (P=0.023), time (P<0.001)] and PP [treatment (P=0.002), time (P<0.001)]. Both FEC and PP were higher in TST calves. There was a 50% reduction in anthelmintic use in TST calves compared to control calves. Clinical signs of lungworm infection, confirmed by the modified Baermann technique, were evident in TST calves on days 62 and 63 of the study. The average daily live weight gain for control and TST calves was 0.50 (0.02)kg day(-1) and 0.47 (0.03)kg day(-1), respectively (P=0.41). Thus, performance in dairy calves can potentially be maintained with fewer anthelmintic treatments but farmers need to be vigilant of the challenge posed by lungworm. Any future approach into the use of TST in FGS calves must take into consideration the relative importance of lungworm as a pathogen.

Effects of phenotypic residual feed intake on response to a glucose tolerance test and gene expression in the insulin signaling pathway in longissimus dorsi in beef cattle.

The objectives of this study were to determine the insulinogenic response to an intravenous glucose tolerance test (GTT) and examine gene expression profiles in the insulin signaling pathway (ISP) in beef animals of differing phenotypic residual feed intake (RFI). Two experiments were conducted. In Exp. 1, a total of 39 Simmental heifers, over 2 yr (yr 1, n = 22, and yr 2, n = 17; mean initial BW = 472 kg [SD = 52.4 kg]), were offered grass silage ad libitum for 104 d. Heifers were subjected to a GTT on d 8 and 65 of the RFI measurement period in yr 1 and 2, respectively. Concentrations of plasma glucose and insulin were measured at -45, -30, -15, 0, 5, 10, 15, 20, 30, 45, 60, 90, 120, 150, and 180 min relative to glucose infusion (0 min). In Exp. 2, a total of 67 Simmental bulls, over 3 yr (yr 1, n = 20; yr 2, n = 33; and yr 3, n = 14; mean initial BW = 431 kg [SD = 63.7 kg]), were offered concentrates ad libitum for 105 d. Biopsies of LM were harvested during the RFI measurement period (yr 1, d 49 and 91; yr 2, d 52 and 92; and yr 3, d 50 and 92). The residuals of the regression of DMI on ADG, midtest metabolic BW (BW(0.75)), and the fixed effect of year, using all animals, were used to compute individual RFI coefficients. Animals were ranked on RFI and assigned to high (inefficient), medium, or low groupings by dividing them into terciles, resulting in 13 heifers and 22, 23, and 22 bulls in their respective RFI groups. In Exp. 1, data from 13 heifers from each of the high- and low-RFI groups, and in Exp. 2, data from the 15 highest and 15 lowest ranking bulls on RFI are reported. In Exp. 1, glucose and insulin response and area under the response curve for glucose and insulin were similar (P > 0.05) between high- and low-RFI heifers. In Exp. 2, no differences (P > 0.05) were found for mRNA expression of 22 genes of the ISP in muscle tissue; however, expression of the transcription factor SREBP1c tended to be positively correlated (r = 0.25, P = 0.07) with RFI. Expression of GLUT4, INPPL1, and SHC increased (P < 0.05) over time, while there was no effect of sample time for any other genes measured. Collectively, these results suggest that insulin response, sensitivity, and associated expression of genes in the ISP within muscle tissue are not contributory factors to variation in RFI. However, further examination of target genes of SREBP1c, which is involved in lipogenesis, may explain some of the biochemical processes underlying variation in phenotypic RFI.

Nematode control in spring-born suckler beef calves using targeted selective anthelmintic treatments.

As anthelmintic resistance is increasingly being reported in cattle worldwide, there is a need to explore alternative approaches to gastrointestinal nematode control in cattle. A novel approach is the use of targeted selective treatments (TST) where only individual animals are treated instead of the entire group. The study objective was to determine if anthelmintic usage could be reduced using a TST-based approach in rotationally grazed first-grazing season suckler beef calves without affecting calf performance. Eighty-eight spring-born suckler beef calves, naïve to anthelmintics, with an initial mean (s.d.) age and live weight of 159 (22.4) days and 221 (42.4) kg, respectively, were used. All calves were vaccinated at pasture against dictyocaulosis at 8 and 12 weeks old. On August 9th 2013 (Week 0), when the trial began, calves were randomised by age, weight, sex, dam breed and sire breed to one of two treatments: (1) standard treatment (positive control) (n=44) and (2) TST (n=44). Samples collected one week prior to the start of the study were used as baseline covariates. Each treatment group was replicated once. All calves in the control groups were treated subcutaneously with levamisole on Week 0 and on Week 6. Individual calves in the TST groups were only eligible for treatment at pasture with the same product if predetermined thresholds were reached [plasma pepsinogen ≥ 2.0 international units of tyrosine/litre and faecal egg count ≥ 200 eggs per gram of faeces]. The trial concluded at housing on Week 13. Data were analysed using repeated measures mixed models ANOVA (PROC MIXED) (SAS 9.3). No calves in the TST groups were treated for gastrointestinal nematodes during the study period as they did not reach pre-determined treatment thresholds. Mean (sem) calf daily live weight gain for control and TST groups was 0.90 (±0.04) and 0.92 (±0.03) kg, respectively (P=0.68). Using an ELISA to detect antibodies to Dictyocaulus viviparus at Week 11, 81% of calves were seropositive. Gastrointestinal nematode challenge in spring-born suckler beef calves under these conditions can potentially be controlled with minimal anthelmintic treatments whilst not significantly impairing calf performance, provided appropriate control measures are taken to prevent dictyocaulosis from occurring.

Grazed grass herbage intake and performance of beef heifers with predetermined phenotypic residual feed intake classification.

Data were collected on 85 Simmental and Simmental × Holstein-Friesian heifers. During the indoor winter period, they were offered grass silage ad libitum and 2 kg of concentrate daily, and individual dry matter intake (DMI) and growth was recorded over 84 days. Individual grass herbage DMI was determined at pasture over a 6-day period, using the n-alkane technique. Body condition score, skeletal measurements, ultrasonic fat and muscle depth, visual muscularity score, total tract digestibility, blood hormones, metabolites and haematology variables and activity behaviour were measured for all heifers. Phenotypic residual feed intake (RFI) was calculated for each animal as the difference between actual DMI and expected DMI during the indoor winter period. Expected DMI was calculated for each animal by regressing average daily DMI on mid-test live weight (LW)(0.75) and average daily gain (ADG) over an 84-day period. Standard deviations above and below the mean were used to group animals into high (>0.5 s.d.), medium (±0.5 s.d.) and low (<0.5 s.d.) RFI. Overall mean (s.d.) values for DMI (kg/day), ADG (kg), feed conversion ratio (FCR) kg DMI/kg ADG and RFI (kg dry matter/day) were 5.82 (0.73), 0.53 (0.18), 12.24 (4.60), 0.00 (0.43), respectively, during the RFI measurement period. Mean DMI (kg/day) and ADG (kg) during the grazing season was 9.77 (1.77) and 0.77 (0.14), respectively. The RFI groups did not differ (P > 0.05) in LW, ADG or FCR at any stage of measurement. RFI was positively correlated (r = 0.59; P < 0.001) with DMI during the RFI measurement period but not with grazed grass herbage DMI (r = 0.06; P = 0.57). Low RFI heifers had 0.07 greater (P < 0.05) concentration of plasma creatinine than high RFI heifers and, during the grazed herbage intake period, spent less time standing and more time lying (P < 0.05) than high RFI heifers. However, low and high RFI groups did not differ (P > 0.05) in ultrasonic backfat thickness or muscle depth, visual muscle scores, skeletal size, total tract digestibility or blood hormone and haematology variables at any stage of the experiment. Despite a sizeable difference in intake of grass silage between low and high RFI heifers during the indoor winter period, there were no detectable differences between RFI groupings for any economically important performance traits measured when animals were offered ensiled or grazed grass herbage.

A reduction in milking frequency and feed allowance improves dairy cow immune status.

Twice-daily milking is the most common milking regimen used globally. A reduction in milking frequency to once daily, combined with a reduced feed allowance (FA), could reduce the physiological stress associated with the transition to peak milk production, and hence improve immune function. This study investigated how milking frequency and FA affect dairy cow immune status. Cows (n = 48) were milked once a day (OAD) or twice a day (TAD) on 1 of 2 FA: high (HFA) or low (LFA), in a 2 × 2 factorial arrangement of treatments. After the mean calving date of March 11, HFA cows were offered ad libitum grass silage and 7 kg of concentrates/cow per day until March 22, then 4 kg of concentrates/cow per day until April 17, and thereafter allocated 31.3 kg of dry matter (DM) grass/cow per day. The LFA cows were offered 4 kg of concentrates/cow per day, 1 kg of concentrates/cow per day, and allocated 19 kg of DM grass/cow per day for the same respective periods. Milk yield was recorded daily and body condition score weekly, and somatic cell count was performed at approximately 2-wk intervals. Blood samples were collected prepartum (d -7 to -1) and at d 1 to 7, d 14 to 21, and d 42 to 49 postpartum. Total and differential leukocyte percentage, IFN-γ production in response to concanavalin A and phytohemagglutinin, and cortisol, haptoglobin (Hp), and serum amyloid A (SAA) concentrations were evaluated. Cows milked OAD had reduced milk yield and body reserve mobilization, but higher somatic cell counts. Milking frequency and diet had no effect on total leukocyte counts. Cows milked OAD had a higher lymphocyte percentage and lower monocyte percentage, and tended to have a lower neutrophil percentage than cows milked TAD. In addition, the LFA cows had a higher eosinophil percentage than cows fed the HFA. Milking frequency and diet had no effect on IFN-γ, Hp, SAA, or cortisol production. Utilization of strategies to reduce milk yield at the beginning of the lactation could not only reduce body reserve mobilization, but also help to maintain a functioning immune system, and thus improve cow welfare.

The effect of transport by road and sea on physiology, immunity and behaviour of beef cattle.

The objective of the study was to investigate the physiological, haematological and immunological responses of weanling heifers transported from Ireland to a feedlot in Spain, and of weanling bulls transported from Ireland to a feedlot in Italy. Physiological variables (including interferon-γ production, cortisol, protein, urea, white blood cell numbers and differentials, and acute phase proteins (haptoglobin and fibrinogen) were used to evaluate the welfare status of animals, before, during and after the respective transport journeys. Age-matched control animals were blood sampled for the same measurements at times corresponding to the transported animals that were retained in Ireland. Heifers transported to Spain lost 7.6% of their initial live weight during the sea crossing to France. However, by the time of their arrival in Spain they had regained 3.3% of their initial live weight and had fully recovered to their pre-transport live weight values within 6 days of arriving in Spain. Weanling bulls lost 7.0% of their live weight during the sea crossing from Ireland to France. The live weight loss in control animals ranged from 1% to 2% during the same period. The percentage of time that bulls spent lying was 63.5% for the sea journey and 35.4% for the journey from the French lairage to the Italian feedlot. The average daily gain (kg) of transported animals was greater (P ≤ 0.05) than control animals from day 11 to 38 (Spain) and day 11 to 40 (Italy), respectively. While transient changes in physiological, haematological and immunological variables were found in the transported and control animals relative to baseline levels, the values were within the normal physiological range for the age and weight of animals involved. Physiological measurements made after the road and sea journeys indicated that the 24h rest in the lairage, with hay and water freely available, allowed animals to recover substantially.