Associations of reproductive indices with fertility outcomes, milk yield, and survival in Holstein cows.

The study is part of a research effort investigating potential associations between genomic variation and fertility of Holstein cows. The objective was to compare the reproductive performance of Holstein cows in 3 categories of 2 reproductive indices (RI) that were developed for the allocation of cows in a ranking for potential fertility, based on the predicted probability of pregnancy. The associations between categories of the developed indices and multiple fertility variables in a large multistate population of Holstein cows were tested. In addition, we analyzed associations among the RI categories with milk yield and survival. Based on phenotypic information from individual cows, 2 reproductive indices (RI1 and RI2) were developed, representing a predicted probability that a cow will become pregnant at first artificial insemination postpartum, as a function of explanatory variables used in a logistic model. Data from a total of 11,733 cows calving in 16 farms located in 4 regions of the United States (Northeast, Midwest, Southeast, and Southwest) were available. Cows were enrolled at parturition and monitored weekly for reproductive events, health status, milk yield, and survival. To develop the indices, potential significant effects were initially tested by univariate analyses. Effects with P ≤ 0.05 were offered to the multivariate analysis, and the final models were determined through backward elimination, considering potentially significant interactions. The final model for RI1 included the random effect of farm and a complement of significant fixed effects as explanatory variables influencing a pregnancy outcome: (1) incidence of retained fetal membranes; (2) metritis; (3) clinical endometritis; (4) lameness at 35 days in milk (DIM); (5) resumption of postpartum ovulation by 50 DIM; (6) season of calving; and (7) parity number. The model for RI2 included (1) parity number; (2) body condition score at 40 DIM; (3) incidence of retained fetal membranes; (4) metritis; (5) resumption of postpartum ovulation by 50 DIM; (6) region; (7) subclinical ketosis; (8) mastitis; (9) clinical endometritis; and (10) milk yield at the first milk test after calving; as well as the interaction effects of postpartum resumption of ovulation by 50 DIM × region; mastitis × region; and milk yield at the first milk test after calving × parity number. Multivariate logistic regression, ANOVA, and survival analysis were used to test the correspondence between the resulting RI and individual fertility, milk yield, and survival from the population. To facilitate the analyses, the resulting RI values were categorized as low for cows in the lowest quartile, medium for cows within the interquartile range, or high for cows in the top quartile. We found consistent agreement between categories of the predicted RI and the measures of fertility and survival collected from individual cows. We conclude that the proposed RI represent a viable approach to refine the allocation of cows into potential low- and high-fertility populations.

Prepartum body condition score and plane of nutrition affect the hepatic transcriptome during the transition period in grazing dairy cows.

BACKGROUND: A transcriptomic approach was used to evaluate potential interactions between prepartum body condition score (BCS) and feeding management in the weeks before calving on hepatic metabolism during the periparturient period. METHODS: Thirty-two mid-lactation grazing dairy cows of mixed age and breed were randomly allocated to one of four treatment groups in a 2 × 2 factorial arrangement: two prepartum BCS categories [4.0 (thin, BCS4) and 5.0 (optimal, BCS5); based on a 10-point scale], and two levels of energy intake during the 3 weeks preceding calving (75 and 125 % of estimated requirements). Liver samples were obtained at -7, 7, and 28 d relative to parturition and subsequent RNA was hybridized to the Agilent 44 K Bovine (V2) Microarray chip. The Dynamic Impact Approach was used for pathway analysis, and Ingenuity Pathway Analysis was used for gene network analysis. RESULTS: The greater number of differentially expressed genes in BCS4 cows in response to prepartum feed allowance (1071 vs 310, over the entire transition period) indicates that these animals were more responsive to prepartum nutrition management than optimally-conditioned cows. However, independent of prepartum BCS, pathway analysis revealed that prepartal feeding level had a marked effect on carbohydrate, amino acid, lipid, and glycan metabolism. Altered carbohydrate and amino acid metabolism suggest a greater and more prolonged negative energy balance postpartum in BCS5 cows overfed prepartum. This is supported by opposite effects of prepartum feeding in BCS4 compared with BCS5 cows in pathways encompassing amino acid, vitamin, and co-factor metabolism. The prepartum feed restriction ameliorates the metabolic adaptation to the onset of lactation in BCS5 cows, while detrimentally affecting BCS4 cows, which seem to better adapt when overfed. Alterations in the glycosaminoglycans synthesis pathway support this idea, indicating better hepatic health status in feed-restricted BCS5 and overfed BCS4 cows. Furthermore, IPA network analysis suggests liver damage in feed-restricted thin cows, likely due to metabolic overload. CONCLUSION: Overall, the data support the hypothesis that overfeeding in late-pregnancy should be limited to underconditioned cows, while cows with optimal degree of body condition should be maintained on an energy-restricted diet.

The effect of calving in the summer on the hepatic transcriptome of Holstein cows during the peripartal period.

The liver is the main metabolic organ coordinating the adaptations that take place during the peripartal period of dairy cows. A successful transition into lactation, rather than management practices alone, depends on environmental factors such as temperature, season of parturition, and photoperiod. Therefore, we analyzed the effect of calving season on the hepatic transcriptome of dairy cows during the transition period. A total of 12 Holstein dairy cows were assigned into 2 groups based on calving season (6 cows March-April, spring; 6 cows June-July, summer, SU). The RNA was extracted from liver samples obtained at -30, 3, and 35 DIM via percutaneous biopsy and hybridized to the Agilent 44K Bovine (V2) Gene Expression Microarray (Agilent Technologies Inc., Santa Clara, CA). A quantitative PCR on 22 target genes was performed to verify and expand the analyses. A total of 4,307 differentially expressed genes were detected (false discovery rate ≤0.05) in SU compared with spring. Furthermore, 73 unique differentially expressed genes were detected in SU compared with spring cows after applying a fold-change threshold ≥3 and ≤-3. For Kyoto Encyclopedia of Genes and Genomes pathways analysis of differentially expressed genes, we used the dynamic impact approach. Ingenuity Pathway Analysis software was used to analyze upstream transcription regulators and perform gene network analysis. Among metabolic pathways, energy metabolism from lipids, carbohydrates, and amino acids was strongly affected by calving in SU, with a reduced level of fatty acid synthesis, oxidation, re-esterification, and synthesis of lipoproteins, leading to hepatic lipidosis. Glycan-synthesis was downregulated in SU cows probably as a mechanism to counteract the progression of this lipidosis. In contrast, calving in the SU resulted in upregulation of gluconeogenesis but also greater use of glucose as an energy source. Among nonmetabolic pathways, the heat-shock response was obviously activated in SU cows but was also associated with inflammatory and intracellular stress response. Furthermore, data support a recent finding that cows experience endoplasmic reticulum stress around parturition. Transcription regulator analysis revealed how metabolic changes are related to important regulatory mechanisms, including epigenetic modification. The holistic analyses of the liver transcriptome response to calving in the summer at high environmental temperatures underscore how transition cows should be carefully managed during this period, as they experience alterations in liver energy metabolism and inflammatory state increasing susceptibility to health disorders in early postpartum.

Brain gene expression changes elicited by peripheral vitellogenin knockdown in the honey bee.

Vitellogenin (Vg) is best known as a yolk protein precursor. Vg also functions to regulate behavioural maturation in adult honey bee workers, but the underlying molecular mechanisms by which it exerts this novel effect are largely unknown. We used abdominal vitellogenin (vg) knockdown with RNA interference (RNAi) and brain transcriptomic profiling to gain insights into how Vg influences honey bee behavioural maturation. We found that vg knockdown caused extensive gene expression changes in the bee brain, with much of this transcriptional response involving changes in central biological functions such as energy metabolism. vg knockdown targeted many of the same genes that show natural, maturation-related differences, but the direction of change for the genes in these two contrasts was not correlated. By contrast, vg knockdown targeted many of the same genes that are regulated by juvenile hormone (JH) and there was a significant correlation for the direction of change for the genes in these two contrasts. These results indicate that the tight coregulatory relationship that exists between JH and Vg in the regulation of honey bee behavioural maturation is manifest at the genomic level and suggest that these two physiological factors act through common pathways to regulate brain gene expression and behaviour.

Feed restriction, but not l-carnitine infusion, alters the liver transcriptome by inhibiting sterol synthesis and mitochondrial oxidative phosphorylation and increasing gluconeogenesis in mid-lactation dairy cows.

Abomasal carnitine infusion during acute feed restriction increases hepatic fatty acid oxidation and decreases liver lipid in dairy cows. Eight mid-lactation Holstein cows were used in a replicated 4×4 Latin square design with 14-d periods. A 2×2 factorial arrangement was used to determine the effects of water infusion+ad libitum dry matter intake (DMI), water infusion+restricted DMI (50% of previous 5-d average), l-carnitine infusion (20 g/d)+ad libitum DMI, or l-carnitine infusion+restricted DMI. Liver RNA from 7 healthy cows was used for transcriptome profiling using a bovine microarray. An ANOVA with a false discovery rate was used to identify treatment and interaction effects. A substantial transcriptome change was observed only with DMI restriction, resulting in 312 (155 downregulated, 157 upregulated) differentially expressed genes. Quantitative PCR was performed to verify microarray data and measure expression of additional genes not present on the microarray. The quantitative PCR data confirmed the effect of feed restriction but not of l-carnitine treatment. Feed restriction increased expression of GPX3 and of genes associated with gluconeogenesis (PC, PDK4), inflammation (SAA3), and signaling (ADIPOR2). In contrast, feed restriction downregulated BBOX, a key for l-carnitine biosynthesis, and the transcription factor HNF4A. The bioinformatics functional analysis of genes affected by DMI restriction uncovered biosynthesis of cholesterol and energy generation by mitochondrial respiration as the most relevant and inhibited functions. The data also indicated an increase of flux toward gluconeogenesis. We interpreted those results as a likely response of the liver to spare energy and provide glucose for the lactating mammary gland during feed deprivation.

Combined effect of purulent vaginal discharge and anovulation on pregnancy status in a large multi-state population of Holstein cows.

The objective of this observational prospective cohort study was to evaluate the combined effect of purulent vaginal discharge (PVD) and anovulation (ANOV) on the reproductive performance of a large multi-state population of Holstein cows. Data were prospectively collected from 11,729 cows in 16 herds located in 4 regions in the United States [Northeast (4 herds), Midwest (6), Southeast (1), and Southwest (5)]. Cows were enrolled at calving and monitored weekly for disease occurrence, reproductive events, and survival. Prevalence of PVD was evaluated at 28 ± 3 d in milk and defined by the presence of mucopurulent to fetid vaginal discharge. Resumption of ovarian cyclicity was determined via transrectal ultrasonography at 40 ± 3 and 54 ± 3 d postpartum. Pregnancy diagnosis was performed by ultrasonography on d 32 ± 3 after artificial insemination (AI) and reconfirmed at d 60 ± 3 of gestation. Pregnancy loss (PL) was defined as a cow diagnosed pregnant at 32 ± 3 but nonpregnant at 60 ± 3 d after AI. The association of PVD and ANOV with pregnancy traits was analyzed using 4 PVD-cyclicity categories that considered the following combinations: NPVD-CYC = absence of PVD and cycling; PVD-CYC = presence of PVD and cycling; NPVD-ANOV = absence of PVD and anovular; and PVD-ANOV = presence of PVD and anovular. Multiple logistic regression and Cox proportional regression were used for the analysis of potential associations between PVD and cyclicity categories and pregnancy at first AI (PAI1), days from calving to pregnancy, and PL at first AI. The odds (95% confidence intervals) of pregnancy increased from cows in the PVD-ANOV category (reference category) to cows in NPVD-ANOV [2.09 (1.62-2.50)], PVD-CYC [2.52 (2.02-3.14)], and NPVD-CYC [3.46 (2.84-4.23)]. Similarly, days from calving to pregnancy were less for NPVD-CYC, followed by PVD-CYC, NPVD-ANOV, and PVD-ANOV (121.4, 137.2, 137.3, and 157.4 d, respectively). On the contrary, no clear association was identified between groups and PL. The results indicate that both PVD and ANOV had a negative impact on PAI1 and days from calving to pregnancy. The results indicated a variable magnitude in the negative impact on the reproductive traits analyzed when both conditions were combined.

Level of nutrient intake affects mammary gland gene expression profiles in preweaned Holstein heifers.

Bovine mammary parenchyma (PAR) and fat pad (MFP) development are responsive to preweaning level of nutrient intake. We studied transcriptome alterations in PAR and MFP from Holstein heifer calves (n=6/treatment) fed different nutrient intakes from birth to ca. 65 d age. Conventional nutrient intake received 441 g of dry matter (DM)/d of a control milk replacer (MR) [CON; 20% crude protein (CP), 20% fat, DM basis]. Calves in the accelerated nutrition groups received 951 g/d of high-protein/low-fat MR (HPLF; 28% CP, 20% fat, DM basis), 951 g/d of high-protein/high-fat MR (HPHF; 28% CP, 28% fat, DM basis), or 1,431 g/d of HPHF (HPHF+) MR. Out of 13,000 genes evaluated, over 1,500 differentially expressed genes (DEG) were affected (false discovery rate <0.10) by level of nutrient intake in PAR or MFP. Feeding HPLF versus CON resulted in the most dramatic changes in gene expression, with 278 and 588 DEG having ≥1.5-fold change in PAR and MFP. In PAR, the most-altered molecular functions were associated with metabolism of the cell (molecular transport and lipid metabolism) with most of the genes downregulated in HPLF versus CON. In MFP, DEG also were primarily associated with metabolism but changes also occurred in genes linked to cell morphology, cell-to-cell signaling, and immune response. Compared with CON, feeding HPHF or HPHF+ did not result in substantial additional effects on DEG beyond those observed with HPLF. The pentose phosphate, mitochondrial dysfunction, and ubiquinone biosynthesis pathways were among the most enriched due to HPLF versus CON in PAR and were inhibited, whereas glycosphingolipid biosynthesis, arachidonic acid metabolism, and eicosanoid synthesis pathways were among the most enriched due to HPLF versus CON in MFP and were inhibited. These responses suggest that, in PAR, doubling nutrient intake from standard feeding rates inhibited energy metabolism and activity of oxidative pathways that partly serve to protect cells against oxidative stress. The MFP in those heifers appeared to decrease production of lipid-derived metabolites that may play roles in signaling pathways within the adipocyte. Overall, results indicated that prepubertal/preweaned mammary transcriptome is responsive to long-term enhanced nutrient supply to achieve greater growth rates before weaning. The biological significance of these results to future milk production remains to be elucidated.

Transcriptional changes in mesenteric and subcutaneous adipose tissue from Holstein cows in response to plane of dietary energy.

BACKGROUND: Dairy cows can readily overconsume dietary energy during most of the prepartum period, often leading to higher prepartal concentrations of insulin and glucose and excessive body fat deposition. The end result of these physiologic changes is greater adipose tissue lipolysis post-partum coupled with excessive hepatic lipid accumulation and compromised health. Although transcriptional regulation of the adipose response to energy availability is well established in non-ruminants, such regulation in cow adipose tissue depots remains poorly characterized. RESULTS: Effects of ad-libitum access to high [HIGH; 1.62 Mcal/kg of dry matter (DM)] or adequate (CON; 1.35 Mcal/kg of DM) dietary energy for 8 wk on mesenteric (MAT) and subcutaneous (SAT) adipose tissue transcript profiles were assessed in non-pregnant non-lactating Holstein dairy cows using a 13,000-sequence annotated bovine oligonucleotide microarray. Statistical analysis revealed 409 and 310 differentially expressed genes (DEG) due to tissue and diet. Bioinformatics analysis was conducted using the Dynamic Impact Approach (DIA) with the KEGG pathway database. Compared with SAT, MAT had more active biological processes related to adipose tissue accumulation (adiponectin secretion) and signs of pro-inflammatory processes due to adipose tissue expansion and macrophage infiltration (generation of ceramides). Feeding the HIGH diet led to changes in mRNA expression of genes associated with cell hypertrophy (regucalcin), activation of adipogenesis (phospholipid phosphatase 1), insulin signaling activation (neuraminidase 1) and angiogenesis (semaphorin 4G, plexin B1). Further, inflammation due to HIGH was underscored by mRNA expression changes associated with oxidative stress response (coenzyme Q3, methyltransferase), ceramide synthesis (N-acylsphingosine amidohydrolase 1), and insulin signaling (interferon regulatory factor 1, phosphoinositide-3-kinase regulatory subunit 1, retinoic acid receptor alpha). Activation of ribosome in cows fed HIGH indicated the existence of greater adipocyte growth rate (M-phase phosphoprotein 10, NMD3 ribosome export adaptor). CONCLUSIONS: The data indicate that long-term ad-libitum access to a higher-energy diet led to transcriptional changes in adipose tissue that stimulated hypertrophy and the activity of pathways associated with a slight but chronic inflammatory response. Further studies would be helpful in determining the extent to which mRNA results also occur at the protein level.

Prepartal Energy Intake Alters Blood Polymorphonuclear Leukocyte Transcriptome During the Peripartal Period in Holstein Cows.

In the dairy industry, cow health and farmer profits depend on the balance between diet (ie, nutrient composition, daily intake) and metabolism. This is especially true during the transition period, where dramatic physiological changes foster vulnerability to immunosuppression, negative energy balance, and clinical and subclinical disorders. Using an Agilent microarray platform, this study examined changes in the transcriptome of bovine polymorphonuclear leukocytes (PMNLs) due to prepartal dietary intake. Holstein cows were fed a high-straw, control-energy diet (CON; NEL = 1.34 Mcal/kg) or overfed a moderate-energy diet (OVE; NEL = 1.62 Mcal/kg) during the dry period. Blood for PMNL isolation and metabolite analysis was collected at -14 and +7 days relative to parturition. At an analysis of variance false discovery rate <0.05, energy intake (OVE vs CON) influenced 1806 genes. Dynamic Impact Approach bioinformatics analysis classified treatment effects on Kyoto Encyclopedia of Genes and Genomes pathways, including activated oxidative phosphorylation and biosynthesis of unsaturated fatty acids and inhibited RNA polymerase, proteasome, and toll-like receptor signaling pathway. This analysis indicates that processes critical for energy metabolism and cellular and immune function were affected with mixed results. However, overall interpretation of the transcriptome data agreed in part with literature documenting a potentially detrimental, chronic activation of PMNL in response to overfeeding. The widespread, transcriptome-level changes captured here confirm the importance of dietary energy adjustments around calving on the immune system.

Effect of altering dose of PG600 on reproductive performance responses in prepubertal gilts and weaned sows.

This study evaluated the effects of altering dose of PG600 on estrus and ovulation responses in prepubertal gilts and weaned sows. Experiment 1 tested the effects of one (1.0x, 400IU eCG+200IU hCG, n=74), one and a half (1.5x, n=82), or two (2.0x, n=71) doses of PG600 for prepubertal gilts. Estrus (58%) and ovulation (90%) were not affected (P>0.10) by dose. Higher doses increased (P<0.01) numbers of corpora lutea (17, 24, and 25), but not (P>0.10) the proportion of gilts with cysts (26, 36, and 46% for 1.0x, 1.5x, and 2.0x, respectively). Experiment 2 tested the effects of 0x (n=30), 0.5x (n=32), 1.0x (n=29), or 1.5x (n=30) doses of PG600 in weaned sows. Dose did not influence return to estrus (90%, P>0.10). There was an effect of dose (P<0.05) on incidence of cysts (3.4, 1.8, 6.4, and 29.8%, for 0x, 0.5x, 1.0x, and 1.5x doses, respectively). The 0.5x dose increased (P<0.01) farrowing rate (83.2%) compared to 0x (72.1%) and 1.5x (58.6%), but was not different from 1.0x (76.4%). Total pigs born (10.5+/-0.8) did not differ (P>0.10) among treatments. These data suggest that increasing dose of PG600 to 1.5x for gilts increases the number of corpora lutea but does not alter the proportion expressing estrus or ovulating. Reducing dose of PG600 for weaned sows did not alter estrus or ovulation, but the 0.5x dose increased farrowing rate compared to no PG600.

Effect of PG600 and adjusted mating times on reproductive performance in weaned sows.

The administration of PG600 to sows at weaning induces >90% of sows to return to estrus within a week, but farrowing rate and litter size are often not improved. This study evaluated the effects of adjusted artificial insemination (AI) times based on weaning to estrus interval (WEI) and estrus to ovulation interval (EOI) following PG600. All sows were given PG600 at weaning and allotted to adjusted (ADJ, n=47) or non-adjusted (NA, n=46) mating times after the onset of estrus. Adjusted mating involved: (1) 2-3 days WEI, AI at 36 h and 48 h; (2) 4 days WEI, AI at 24h and 36 h; (3) 5 days WEI, AI at 12h and 24h; and (4) 6-7 days WEI, AI at 0 h and 12h. Mating for NA occurred at 0 h and 24h after onset of estrus. There was no effect of treatment on return to estrus (92.9% versus 92.5%) or ovulation (92.7% versus 92.5% for ADJ and NA, respectively). The proportion of first AI occurring within 24h prior to ovulation was increased (83.8% versus 50.0%) and closer to ovulation for ADJ compared to NA treatment (19.4h versus 27.3h, P<0.05). Treatment did not influence (P>0.10) the proportion of second AI occurring within 24h of ovulation (72.8% versus 56.6%) but did influence (P<0.05) the interval from second AI to ovulation for ADJ compared to NA (10.6h versus 3.3h). The ADJ treatment increased (P<0.05) the proportion of sows that received an AI within 24h before ovulation (98.8% versus 87.0%). However, treatment did not influence pregnancy (87.4%) or farrowing (79.5%) rates but the NA treatment tended to increase (P<0.10) total number of pigs born (11.8 versus 8.9). In conclusion, while AI times for ADJ appeared to occur within optimal periods, farrowing rates were not improved and litter size decreased, suggesting that two AI at 12h intervals and closer to the time of ovulation may be detrimental. Overall, these data suggest that for sows injected with PG600 at weaning and receiving two AI, breeding at 0 h and 24h after onset of estrus is recommended.

Genetic gain and economic values of selection strategies including semen traits in three- and four-way crossbreeding systems for swine production.

Four semen traits: volume (VOL), concentration (CON), progressive motility of spermatozoa (MOT), and abnormal spermatozoa (ABN) provide complementary information on boar fertility. Assessment of the impact of selection for semen traits is hindered by limited information on economic parameters. Objectives of this study were to estimate economic values for semen traits and to evaluate the genetic gain when these traits are incorporated into traditional selection strategies in a 3-tier system of swine production. Three-way (maternal nucleus lines A and B and paternal nucleus line C) and 4-way (additional paternal nucleus line D) crossbreeding schemes were compared. A novel population structure that accommodated selection for semen traits was developed. Three selection strategies were simulated. Selection Strategy I (baseline) encompassed selection for maternal traits: number of pigs born alive (NBA), litter birth weight (LBW), adjusted 21-d litter weight (A21), and number of pigs at 21 d (N21); and paternal traits: number of days to 113.5 kg (D113), backfat (BF), ADG, feed efficiency (FE), and carcass lean % (LEAN). Selection Strategy II included Strategy I and the number of usable semen doses per collection (DOSES), a function of the 4 semen traits. Selection Strategy III included Strategy I and the 4 semen traits individually. The estimated economic values of VOL, CON, MOT, ABN, and DOSES for 7 to 1 collections/wk ranged from $0.21 to $1.44/mL, $0.12 to $0.83/10 spermatozoa/mm, $0.61 to $12.66/%, -$0.53 to -$10.88/%, and $2.01 to $41.43/%, respectively. The decrease in the relative economic values of semen traits and DOSES with higher number of collections per wk was sharper between 1 and 2.33 collections/wk than between 2.33 and 7 collections/wk. The higher economic value of MOT and ABN relative to VOL and CON could be linked to the genetic variances and covariances of these traits. Average genetic gains for the maternal traits were comparable across strategies. Genetic gains for paternal traits, excluding semen traits, were greater in selection Strategy I than Strategies III and II. Genetic gains for paternal and maternal traits were greater in the 4- and 3-way schemes, respectively. The selection strategy including the 4 semen traits is recommended because this approach enables genetic gains for these traits without compromising the genetic gains for maternal traits and with minimal losses in genetic gains for paternal traits.

Enhanced fertility prediction of cryopreserved boar spermatozoa using novel sperm function assessment.

Due to reduced fertility, cryopreserved semen is seldom used for commercial porcine artificial insemination (AI). Predicting the fertility of individual frozen ejaculates for selection of higher quality semen prior to AI would increase overall success. Our objective was to test novel and traditional laboratory analyses to identify characteristics of cryopreserved spermatozoa that are related to boar fertility. Traditional post-thaw analyses of motility, viability, and acrosome integrity were performed on each ejaculate. In vitro fertilization, cleavage, and blastocyst development were also determined. Finally, spermatozoa-oviduct binding and competitive zona-binding assays were applied to assess sperm adhesion to these two matrices. Fertility of the same ejaculates subjected to laboratory assays was determined for each boar by multi-sire AI and defined as (i) the mean percentage of the litter sired and (ii) the mean number of piglets sired in each litter. Means of each laboratory evaluation were calculated for each boar and those values were applied to multiple linear regression analyses to determine which sperm traits could collectively estimate fertility in the simplest model. The regression model to predict the percent of litter sired by each boar was highly effective (p < 0.001, r(2) = 0.87) and included five traits; acrosome-compromised spermatozoa, percent live spermatozoa (0 and 60 min post-thaw), percent total motility, and the number of zona-bound spermatozoa. A second model to predict the number of piglets sired by boar was also effective (p < 0.05, r(2) = 0.57). These models indicate that the fertility of cryopreserved boar spermatozoa can be predicted effectively by including traditional and novel laboratory assays that consider functions of spermatozoa.

Survival analysis of lamb mortality in a terminal sire composite population.

Records of mortality during the first year of life of 8,642 lambs from a composite population at the U.S. Meat Animal Research Center were studied using survival and logistic analyses. The traditional logistic approach analyzes the binary response of whether or not a lamb survived until a particular time point, thus disregarding information on the actual age at death. Survival analysis offers an alternative way to study mortality, wherein the response variable studied is the precise age at death while accounting for possible record censoring. Lamb mortality was studied across five periods based on management practices: birth to weaning, birth to 120 d of age, birth to 365 d of age, weaning to 365 d of age, and 120 to 365 d of age. Explanatory variables included in the models were sex, type of birth, age of dam, and whether or not a lamb was raised in a nursery. The survival analysis was implemented using Weibull and Cox proportional hazards models with sire as random effect. The logistic approach evaluated sire, animal, and maternal effects models. Lambs culled during any period were treated as censored in the survival analyses and were assumed alive in the logistic analyses. Similar estimates of the explanatory variables were obtained from the survival and logistic analyses, but the survival analyses had lower standard errors than the logistic analyses, suggesting a slight superiority of the former approach. Heritability estimates were generally consistent across all periods ranging from 0.15 to 0.21 in the Weibull model, 0.12 to 0.20 in the Cox model, 0.08 to 0.11 in the logistic sire model, 0.04 to 0.05 in the logistic animal model, and 0.03 to 0.07 in the maternal effects logistic model. Maternal effects were important in the early stages of lamb life, but the maternal heritability was less than 0.07 in all the stages studied with a negative correlation (-0.86 to -0.61) between direct and maternal effects. The estimates of additive genetic variance indicate that the use of survival analysis estimates in breeding schemes could allow for effective selection against mortality, thereby improving sheep productivity, welfare, and profitability.

Competing risks analysis of lamb mortality in a terminal sire composite population.

Mortality records from birth to weaning of 8,301 lambs from a composite population at the U.S. Meat Animal Research Center were analyzed using a competing risks model. The advantage of the competing risks model over traditional survival analyses is that different hazards of mortality can be assigned to different causes, such as disease, dystocia, and starvation. In this study, specific causes of mortality were grouped into dam-related (DAMR; e.g., dystocia and starvation), pneumonia (PNEU), disease (DIS; excluding pneumonia), and other (OTHER) categories. The hazard of mortality was analyzed using a competing risk approach, where each mortality category was assumed to be independent. Continuous- and discrete-time survival analyses were implemented using sire, animal, and maternal effects mixed models. The continuous-time survival analysis used the Weibull model to describe the hazard of mortality for each category of mortality. Under the discrete-time survival analysis, a complementary log-log link function was used to analyze animal-time data sets using weekly intervals for each category of mortality. Explanatory variables were sex, type of birth, contemporary group, and age of dam. The significant influences of type of birth and age of dam effects were consistent across category of mortality, and the sex effect was significant for all categories except the OTHER category. Estimates of variance components indicated strong maternal effects for all categories except for PNEU. Estimates of additive genetic heritabilities from the discrete maternal effects models were 0.08+/-0.04, 0.09+/-0.18, 0.16+/-0.12, 0.19+/-0.09, and 0.14+/-0.10 for OVERALL (all causes combined), DIS, DAMR, PNEU, and OTHER categories, respectively. Ignoring the cause of the defining event in mortality and longevity studies may hide important genetic differences. Therefore, the effectiveness of breeding programs relying on models that ignore multiple causes of an event in time-to-event data, such as mortality and longevity, could be affected.

Discrete time survival analysis of lamb mortality in a terminal sire composite population.

Mortality records of 8,642 lambs from a composite population at the U.S. Meat Animal Research Center during the first year of life were studied using discrete survival analyses. Lamb mortality was studied across periods from birth to weaning, birth to 365 d of age, and weaning to 365 d of age. Animal-time data sets were created for each period using different time intervals: daily, weekly, fortnightly, and monthly. Each data set was analyzed using logistic and complementary log-log sire, animal, and maternal effects models. Explanatory variables included in the models were duration of time interval, sex, type of birth, contemporary group, age of dam, and type of upbringing (nursery or not). Similar estimates of explanatory variables were obtained within the same period across models and different time intervals. Heritability estimates from the complementary log-log models were greater than those from the comparable logistic models because of the difference in variance of the respective link functions. Heritability estimates from the complementary log-log sire model ranged from 0.13 to 0.21 for all periods. These estimates were greater than the complementary log-log animal model estimates that ranged from 0.04 to 0.12. Maternal effects were important early in life, with the maternal heritability slightly greater than the direct additive heritability. Negative correlations (-0.72 to -0.65) between direct additive and maternal effects was estimated. The similarity of results among survival analysis methods demonstrates that the discrete methodology is a viable alternative to estimate variance components in livestock survival data.

Effect of subcutaneous vs intramuscular administration of P.G. 600 on estrual and ovulatory responses of prepubertal gilts.

The effects of s.c. and i.m. administration of P.G. 600 on estrual and ovulatory responses of prepubertal gilts were investigated. One hundred eighty-four crossbred gilts between 159 and 174 d of age were assigned to receive P.G. 600 s.c. (s.c. P.G. 600) in the flank, P.G. 600 i.m. in the neck (i.m. P.G. 600), or no treatment (control). At the beginning of the study (d 0), animals were selected from a modified, open-front barn, regrouped, relocated to new pens, and exposed once daily to a mature boar to check for estrus. On d 17, ovaries were collected from all gilts and analyzed for the presence of corpora lutea (CL), cystic follicles, and cystic CL. A higher proportion of gilts expressed estrus with s.c. P.G. 600 (76%) than with i.m. P.G. 600 (52%, P < .01) or controls (15%, P < .01). The interval from initiation of treatment on d 0 to estrus was reduced (P < .01) by P.G. 600 (4.6 d) compared to controls (5.9 d), but there was no significant difference between P.G. 600 treatments. Both s.c. P.G. 600 (86%) and i.m. P.G. 600 (77%) induced more gilts to ovulate (P < .01) than controls (18%), but there was no significant difference between P.G. 600 treatments. No significant effect of treatment was detected on number of CL (17.9), number of cystic follicles (1.5), or number of cystic CL (2.1). Proportions of gilts that developed cystic follicles or cystic CL were not influenced by treatment. Results of this study indicated that s.c. administration of P.G. 600 significantly improved the induction of estrus in prepubertal gilts compared to i.m. administration.