Genetic and environmental effects on early growth and performance in purebred Holstein, Jersey, and reciprocal crossbred calves.

For this designed experiment, Holstein × Holstein (n=28), Jersey × Jersey (n=10), Holstein × Jersey (n=15), and Jersey × Holstein (n=15) bull and heifer calves were compared for body weight (BW), dry matter intake, feed efficiency, hip height, BW gain to 42 and 56 d, and days to weaning from birth to 8 wk. All traits were examined for purebred, maternal, and heterotic genetic effects. Purebred genetic effects significantly favored the Holstein breed for BW, dry matter intake, hip height, and BW gain to 42 and 56 d. Heterotic genetic effects were present for dry matter intake and hip height. Calf sex affected BW and BW gain to 56 d. Our results indicate that early calf growth is influenced primarily by purebred effects favoring the Holstein breed and to a lesser extent heterosis.

Effects of Cryptosporidium parvum infection on lymphocyte phenotype and reactivity in calves.

Cryptosporidium parvum is a protozoan parasite now recognized as a significant cause of neonatal diarrhea in calves, and infection is also widespread in both immunocompetent and immunocompromised humans. No effective treatment or preventive measures against C. parvum infection are available, owing largely to the lack of understanding of immunologic mechanisms of resistance to and recovery from this parasite. In the present study, we compared phenotypes of lymphocytes from peripheral blood, spleen, mesenteric, and prescapular lymph nodes of calves infected or not infected with C. parvum. We also compared reactivity of these lymphocytes to mitogens and C. parvum antigen in vitro. There were more non-T, non-B (null) lymphocytes in all tissues of infected compared with control calves. The percent of CD8+ lymphocytes was significantly increased in spleens of infected compared with control calves, and there were markedly less CD4+ than CD8+ cells in spleens of both groups (i.e. low CD4/CD8 ratios). Splenic lymphocytes showed significantly decreased in vitro proliferation to pokeweed mitogen and C. parvum antigen stimulation compared with lymphocytes from other tissues. These findings suggest that null lymphocytes and CD8+ lymphocytes may be important in the expression and regulation of bovine immune responses to C. parvum in vivo.

In vitro modulation of proliferation and phenotype of resting and mitogen-stimulated bovine mononuclear leukocytes by 1,25-dihydroxyvitamin D3.

Effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the proliferation and phenotype of normal bovine peripheral blood mononuclear leukocytes (MNL) were studied in vitro. Resting and pokeweed mitogen (PWM)-stimulated MNL cultures were supplemented with 1.0 nM of 1,25(OH)2D3 at the beginning of the culture period. Leukocytes were removed from 2-, 4-, 6-, 8-, 10-, 12-, and 14-day unsupplemented and 1.25(OH)2D3-supplemented cultures, and were counted and phenotyped using monoclonal antibodies to bovine leukocyte surface antigens. Cell numbers in resting MNL cultures decreased with time and were unaffected by 1,25(OH)2D3 supplementation. The progressive increase in cell numbers in PWM-stimulated MNL cultures was suppressed, but not abolished by 1,25(OH)2D3. Suppression was greatest in PWM-stimulated 6- to 12-day cultures. Cellular composition of resting MNL cultures was unaffected by 1,25(OH)2D3. Pokeweed mitogen-stimulated cultures supplemented with 1,25(OH)2D3 had fewer total T-cells and CD4+ T-cells at 6-14 days. In contrast, numbers of CD8+ T-cells were significantly higher in 1,25(OH)2D3-supplemented cultures at 6, 10, and 14 days. Effects of 1,25(OH)2D3 on CD4+ and CD8+ T-cell populations were manifested by a significant reduction in the CD4+:CD8+ T-cell ratios in 6- to 14-day cultures. Proliferation of IL-2 receptor+ and MHC class II antigen+ cells was also reduced in supplemented 6- to 14-day cultures, indicating events associated with PWM-induced MNL activation were suppressed by 1,25(OH)2D3. These findings indicate that 1,25(OH)2D3 modulates the proliferation and differentiation of bovine MNL in vitro. Our results also suggest that changes in plasma or tissue 1,25(OH)2D3 concentrations that occur during the peripartum period and in clinical cases of milk fever may regulate the bovine immune system in vivo.

Effects of supplemental vitamin A on retinoic acid concentrations in the plasma of preruminant calves.

Neonatal calves are fed frequently milk replacers with vitamin A concentrations exceeding those recommended by the National Research Council. The vitamin A metabolite, retinoic acid (RA), affects profoundly cellular differentiation and homeostasis. For this reason, effects of dietary vitamin A on plasma concentrations of RA isomers in milk replacer-fed calves were examined. Male, Holstein calves (n = 24) were fed colostrum within 12 hours after birth and, thereafter, a custom-formulated low vitamin A milk replacer providing 0, 1700 [National Research Council (NRC) daily requirement for young growing calves] (controls), 34,000 (industry standard in the United States) or 68,000 IU of vitamin A daily. Concentrations of retinol and RA isomers in plasma samples collected from birth to 27 days of age were determined by HPLC. Retinol was affected by dietary vitamin A with higher concentrations occurring in calves supplemented with > or = 34,000 IU of vitamin A/day than in control (1700 IU of vitamin daily) and unsupplemented calves. Relative to controls, concentrations of all isomers of RA were higher in calves supplemented with > or = 34,000 of vitamin A daily during the experimental period. The predominant isomer in all calves was 9,13-dicis-RA. In control calves, 9,13-dicis-RA and 9-cis-RA were maximal at 1 to 6 days of age and then decreased progressively. In calves fed > or = 34,000 IU of vitamin A daily, concentrations of these isomers were markedly higher at 6 days of age, relative to controls, and remained elevated for the duration of the study. In all calves, retinol was correlated positively with 9,13-dicis- and 9-cis-RA from 9 to 27 days of age. 9,13-cis-Retinoic acid was correlated positively with 9-cis- and 13-cis-RA from 13 to 27 days of age. It is concluded that supplementing milk replacer-fed calves with vitamin A at levels exceeding current NRC recommendations by > or = 20-fold causes an elevation in plasma concentrations of retinol and retinoic acids. 9,13-dicis- and 9-cis-Retinoic acids were most affected by supplemental vitamin A. Physiologic consequences of increased plasma RA concentrations induced by high dietary levels of vitamin A warrant investigation.

Immune parameters of dry cows fed mannan oligosaccharide and subsequent transfer of immunity to calves.

The objective of this study was to evaluate the benefits of supplementation of mannan oligosaccharide (MOS) to cows during the last 3 wk of the dry period on immune function of the cows and subsequent transfer of passive immunity to their calves. Indicators of nonspecific and specific immunity were evaluated. Cows were vaccinated against rotavirus at 4 and 2 wk before expected parturition. Blood samples were obtained from cows before vaccination and at weekly intervals until calving and from calves at birth and 24 h for analysis of serum protein concentrations, packed cell volume, white blood cell counts, white blood cell differentials, and serum rotavirus neutralization titers. Colostrum quantity and quality were measured at calving, and immunoglobulin isotype concentrations in colostrum were determined. Specific immunity was enhanced by MOS supplementation as evidenced by greater serum rotavirus neutralization titers at calving in cows supplemented with MOS compared with control cows. Colostral rotavirus neutralization titers were not affected by treatment. Although numerical differences appeared large, there was a high degree of variability in the colostral rotavirus neutralization titers. Calves from cows fed MOS tended to have greater serum rotavirus neutralization titers compared with calves from cows fed the control diet. There was a tendency for greater increases in serum protein concentrations from birth to 24 h in calves from cows fed MOS compared with calves from cows fed the control diet. Results indicate that supplementation of MOS to cows during the dry period enhanced their immune response to rotavirus and tended to enhance the subsequent transfer of rotavirus antibodies to calves.

Retinoid-induced modulation of immunoglobulin M secretion by bovine mononuclear leukocytes in vitro.

Effects of trans and cis isomers of retinol and retinoic acid on IgM secretion by bovine peripheral blood mononuclear leukocytes were evaluated in vitro. Mononuclear leukocyte cultures that were unstimulated or stimulated by pokeweed mitogen were supplemented with isomers of retinol and retinoic acid at 10(-10) to 10(-6) M. Concentrations of polyclonal IgM in supernatants from 14-d cultures were measured by an ELISA. Cultures stimulated by pokeweed mitogen consistently secreted more IgM than parallel, unstimulated cultures. Retinoid supplementation did not affect basal IgM secretion by unstimulated cultures. However, each retinoid affected IgM secretion by cultures stimulated by mitogen. The nature of the effect was dependent on the concentration of the specific retinoid. All-trans-retinoic acid enhanced secretion at 10(-10) M and inhibited secretion at 10(-6) M. The other retinoids, however, did not inhibit IgM secretion at any concentration. Each retinoid enhanced IgM secretion at one or more concentrations, although enhancement was produced by much lower concentrations of retinoic acid isomers than retinol isomers. These results indicate that retinol and retinoic acid modulate polyclonal IgM secretion by cultures of bovine mononuclear leukocytes stimulated by mitogen. Future research will determine which subsets of the mononuclear leukocyte population are affected and whether trans-retinoic acid is the metabolite that produces these effects.

Effects of ketones, acetate, butyrate, and glucose on bovine lymphocyte proliferation.

Blood leukocytes from age-matched heifers were used to determine effects of ketones, acetate, butyrate, and glucose on in vitro lymphocyte proliferation. Lymphocytes stimulated with concanavalin A, phytohemagglutinin-P, or pokeweed mitogen were cultured in the presence or absence of beta-hydroxybutyrate, acetoacetate, acetone, acetate, butyrate, and glucose. Only supraphysiological levels of beta-hydroxybutyrate inhibited proliferation in cultures of mitogen-stimulated lymphocytes, whereas mixtures of beta-hydroxybutyrate and acetoacetate at levels seen in severe ketosis stimulated concanavalin A and phytohemagglutinin-P-driven proliferation. Because acetoacetate was a lithium salt, lithium chloride served as a negative control. Results suggest the enhanced proliferation by cultures containing lithium acetoacetate was due to lithium, not acetoacetate. Butyrate (at concentrations greater than seen in bovine plasma) and acetate at normal levels inhibited proliferation. Concanavalin A- and pokeweed-mitogen-driven proliferation was greater in cultures containing lower glucose levels, but acetate added to cultures containing low glucose inhibited concanavalin A-stimulated proliferation. Proliferation by pokeweed mitogen-stimulated cultures containing acetate, beta-hydroxybutyrate, and acetoacetate was suppressed at the lower concentrations of glucose tested. In conclusion, ketones, butyrate, and glucose at concentrations occurring in vivo had minimal effects on bovine lymphocyte proliferation in vitro. Levels of acetate associated with ketosis suppressed lymphocyte function and may alter immune responsiveness in vivo.

Influence of vitamin A supplementation in milk on growth, health, concentrations of vitamins in plasma, and immune parameters of calves.

Seventy-seven Holstein calves were used to determine effects of vitamin A supplementation (0, 15,000, or 30,000 IU/d) of milk fed to calves through 6 wk of age. Effects of gender of calves and parity of dams also were considered. Supplementation with vitamin A did not affect retinol concentrations in plasma; however, calves fed milk containing supplemental vitamin A had decreased alpha-tocopherol concentrations in plasma at 6 wk compared with the concentrations in plasma of calves that were fed milk without supplemental vitamin A. Growth, serum protein, serum immunoglobulin (Ig) M and IgG, leukocyte proportions, and weekly fecal scores were not affected by vitamin A supplementation. Calves that scoured were fed milk supplemented with an additional 0 or 30,000 IU/d of vitamin A. Supplementation with an additional 30,000 IU/d when calves were scouring increased treatment days. Female calves had lower body measurements (weight, length, and height) at birth and greater fecal scores for wk 2 and 3 than did male calves. Gender did not affect serum protein, IgM, or IgG; however, female calves had higher percentages of monocytes and lower percentages of T cells than did male calves. At 6 wk, female calves also had higher percentages of B cells than did male calves. These data indicate that ratios of vitamins A and E should be considered in dietary formulations for calves. Also, additional vitamin A provided by some scour treatments could be detrimental to calves that are already receive vitamin A supplementation.

Proliferation and phenotype of bovine mononuclear leukocytes in cultures stimulated by pokeweed mitogen.

Cell proliferation and phenotype were evaluated at 2, 4, 6, 8, 10, 12, and 14 d in cultures of bovine peripheral blood mononuclear leukocytes stimulated by pokeweed mitogen. Cell numbers in unstimulated and stimulated 2-d cultures decreased to about 45% of the number originally added. Cell numbers at 6 d in stimulated cultures increased to 96% of the number originally seeded and remained elevated from 6 to 14 d in cultures. In contrast, numbers in unstimulated cultures at 4 to 14 d decreased; < 20% of the original number remained at 14 d. The increase in cell numbers in stimulated cultures from 4 and 6 d was due primarily to an increase in CD2+ T cells, specifically the CD4+ T-cell subset. Proliferation of interleukin-2 receptor+ and major histocompatibility class II antigen+ cells increased in these cultures. Expression of these antigens decreased in unstimulated cultures. The B-cell numbers in stimulated cultures at 2 to 4 d increased and then stabilized. Concentrations of IgM in stimulated 14-d cultures were 5 to 15 times those in parallel unstimulated cultures. Overall, IgM secretion induced by pokeweed mitogen by B cells in cultures of bovine mononuclear leukocyte is associated with proliferation of CD4+ (helper-inducer) T cells, B cells, and increased expression of activation antigens.

Leucine and its catabolites alter mitogen-stimulated DNA synthesis by bovine lymphocytes.

This study determined effects of leucine and its catabolites on in vitro, mitogen-stimulated DNA synthesis by bovine lymphocytes. Cultures grown in leucine-free or leucine-replete (0.4 mmol/L leucine) medium were supplemented with 0-10.0 mmol/L leucine or individual catabolites. Leucine at greater than or equal to 0.08 mmol/L was necessary for normal DNA synthesis by mitogen-stimulated bovine lymphocytes. beta-Hydroxy-beta-methylbutyrate (HMB) and beta-hydroxy-beta-methylglutarate (HMG) had minimal effect on unresponsiveness of mitogen-stimulated bovine lymphocytes in leucine-free medium; however, alpha-ketoisocaproate (KIC) at 0.4 and 2.0 mmol/L partially or completely restored DNA synthesis. In leucine-replete medium, 0.016-0.4 mmol/L KIC and 0.016-2.0 mmol/L HMB and HMG did not affect DNA synthesis. At 2.0 and 10.0 mmol/L, KIC inhibited (P less than 0.01) DNA synthesis, whereas HMB and HMG at 10.0 mmol/L enhanced (P less than 0.01) DNA synthesis. Overall, these results suggest that leucine is necessary for mitogen-induced DNA synthesis by bovine lymphocytes, and that this requirement for leucine can be partially met by KIC. When leucine was not limiting, KIC, HMB and HMG at concentrations that might occur in vivo did not alter lymphocyte DNA synthesis in vitro.

Effects of ketones, acetate, and glucose on in vitro immunoglobulin secretion by bovine lymphocytes.

Individual and combined effects of ketones, acetate, and glucose on IgM secretion by bovine blood lymphocytes were evaluated in vitro. Supernatants from 14-d cultures of unstimulated and mitogen- or antigen-stimulated mono-nuclear leukocytes were harvested and analyzed for total and antigen-specific IgM. Ketones, acetate, and 1,3-butanediol individually added up to 6.25 mM had no effect on total IgM secreted by cells grown in medium containing 11.1 mM glucose. However, butyrate at 6.25 mM inhibited IgM secretion. Addition of a mixture of ketones approximating plasma levels of severely ketotic cows inhibited mitogen-induced IgM secretion in 11.1 mM glucose-supplemented cultures. Results from experiments evaluating effects of glucose concentrations on IgM secretion indicated that plasma glucose concentration associated with the ketotic state (1.66 mM), compared with normal plasma glucose concentration (3.33 mM), did not affect total or antigen-specific IgM secretion. Supplementation of cultures containing up to 3.33 mM glucose with ketones, acetate, or both either had no effect or a modest stimulatory effect. These data indicate that effects of ketones and acetate on IgM secretion are dependent on the concentration of glucose in culture and suggest that changes in plasma glucose, ketone, and acetate concentrations associated with bovine ketosis do not alter IgM secretion in vivo.

Use of the relative dose response (RDR) assay to determine vitamin A status of calves at birth and four weeks of age.

An accurate assessment of vitamin A status can be determined by analysis of liver biopsy samples; however, liver biopsies are not always feasible. Plasma concentrations of vitamin A do not provide an accurate indication of vitamin A status. The objective of this study, therefore, was to determine the ability of the relative dose response assay to indicate the vitamin A status of Holstein calves. Calves were obtained at birth and assigned to vitamin A treatments (0, 1700, 34,000, or 68,000 IU/d) added to milk replacer. Liver biopsies and relative dose response assays were performed at birth and 4 wk. Calves supplemented with 1700, 34,000, or 68,000 IU of vitamin A/d had adequate (greater than 20 microg/g) liver concentrations of vitamin A at 4 wk of age. The relative dose response assay at 4 wk was correlated with liver concentrations of vitamin A. Both the relative dose response assay and liver concentrations of vitamin A indicated that calves not supplemented with vitamin A had low vitamin A status, whereas other treatment groups had adequate vitamin A status. Plasma concentrations of retinol increased by 4 wk of age in calves receiving supplemental vitamin A at 34,000 IU and 68,000 IU/d and decreased in unsupplemented calves; however, all calves had concentrations of <20 microg of retinol/dl of plasma. The relative dose response assay agreed with liver biopsies as an indication of vitamin A status, whereas plasma concentrations of retinol incorrectly indicated all treatment groups were deficient in vitamin A.

Growth and health of Holstein calves fed milk replacers supplemented with antibiotics or Enteroguard.

Forty-five Holstein calves were fed milk replacers containing either antibiotics [MRA (oxytetracycline at 138 mg/kg and neomycin at 276 mg/kg), n = 22)] or Enteroguard [MRE, a blend of fructooligosaccharides, allicin, and gut-active microbes at (129 mg/kg, n = 23)] from birth to 5 wk of age to compare effects on average daily gain and on incidence of scours. Performance was evaluated by measuring weight gain, feed efficiency, and fecal scores. The overall body weight gains and severity of scours were not different between treatments, nor were there differences in starter intake or mean body weight gain. During wk 2, the average gain of calves fed MRA was less than that of calves fed MRE (0.07 vs. 0.09 kg/d, P = 0.09), and greater during wk 5 (0.62 vs. 0.51 kg/d, P < 0.01); however, total gain for calves fed MRE was not different from calves fed MRA. Likewise, average feed efficiencies (gain/dry matter intake) were not different. Severity of scours, as measured by fecal scores, and concentrations of serum proteins, an indirect measure of immunoglobulins, were similar for calves fed MRA and MRE. The results suggest that antibiotics in milk replacers can be replaced with compounds such as fructooligosaccharides, probiotics, and allicin to obtain similar calf performance.

Administration of 13-cis-retinoic acid to dairy cattle. 2. Phenotype of blood leukocytes and production of immunoglobulin.

Eight Holstein dairy cattle were assigned randomly to treatments in three replicate experiments evaluating the effects of 13-cis-retinoic acid on mononuclear leukocyte function. Treatments were i.m. injections of 0 (vehicle only), 100, 200, or 400 mg/d of 13-cis-retinoic acid in dimethylsulfoxide for 7 consecutive d. Peripheral blood was collected before treatment and periodically for 18 d after initiation of treatments. Parameters measured were IgM production in vitro by blood lymphocytes, serum Ig concentrations, and the phenotype of peripheral blood mononuclear leukocytes. Administration of 13-cis-retinoic acid had no effect on in vitro Ig production induced by pokeweed mitogen; however, supplementation of the same cultures with 13-cis-retinoic acid enhanced production of polyclonal IgM. Serum Ig concentrations and total numbers of peripheral blood leukocytes and numbers within mononuclear leukocyte subsets were unaffected by treatment with 13-cis-retinoic acid. Experimentally induced elevations in the concentrations of serum and intracellular retinoic acids did not affect mononuclear leukocyte function in vivo.

Effect of vitamins A and E on nitric oxide production by blood mononuclear leukocytes from neonatal calves fed milk replacer.

This study evaluated the effects of dietary vitamin A and E on the in vitro capacity of blood mononuclear leukocytes from calves to produce nitric oxide. Calves fed milk replacer received 100 IU/d of vitamin E as RRR-alpha-tocopherol or RRR-alpha-tocopheryl acetate and 0, 1700, 34,000, or 68,000 IU of vitamin A as retinyl acetate. Leukocytes from calves produced greater amounts of nitric oxide relative to leukocytes from adult cattle. The greater production of nitric oxide by calf leukocytes may be typical of the immature neonatal immune system. Nitric oxide production by calves fed RRR-alpha-tocopherol and either 1700 or 34,000 IU of vitamin A was less than that of calves in other groups and was more typical of production by leukocytes from cows. Our data suggest that optimal amounts of dietary vitamins A and E prompt the maturation of this response toward one that is more typical of adult cattle. Leukocytes from 1-wk-old calves produced less nitric oxide and were less responsive to stimuli than were leukocytes from older calves, a possible consequence of suppressive factors that were present in the ingested colostrum or in the circulation at birth.

Health and performance of Holstein calves that suckled or were hand-fed colostrum and were fed one of three physical forms of starter.

Intake of colostrum by neonatal calves and early transition to calf starter are two important factors in successful calf programs. Thirty-one Holstein calves were used to determine health and performance of calves that were 1) allowed to remain with their dams for 3 d and suckle (suckled calves) or were removed from their dams and fed colostrum only by bottle (bottle calves); and were 2) fed ground, pelleted, or textured starters, formulated to be isonitrogenous. Bottle calves were removed from their dams at birth, fed 2.84 L of colostrum, placed in individual hutches, and fed 1.89 L of colostrum 12 h after the first feeding. Suckled calves were removed from their dams after 3 d and placed in individual hutches. Once calves were housed in hutches, they were fed 2 L of whole milk twice daily and were provided starters and water beginning on d 3. Calves were weighed at birth and weekly for 6 wk. Blood samples were obtained at birth, 24 h, and weekly for serum protein determination. Starter intake, fecal scores, and electrolyte treatments were recorded daily. Weaning began when calves had consumed 0.68 kg starter for 2 d consecutively. There were no differences in treatment means between suckled and bottle calves for total gain, grain consumption, days with fecal scores >2, or electrolyte treatments per calf. Average days to weaning was greater for bottle calves compared with suckled calves. Mean serum protein concentration at 24 h was greater for bottle (6.0 g/dl) compared with suckled calves (5.8 g/dl) and only 2 of 15 bottle calves had serum protein concentrations <5.0 g/dl compared with 6 of 16 suckled calves. For starter treatments, calves fed textured starter consumed more total grain, were weaned earlier, and weighed more at 6 wk of age than calves fed pelleted starter. Based on 24-h serum protein concentrations, transfer of passive immunity was greater for bottle calves compared with suckled calves.

The effect of cation-anion difference on calcium requirement, feed intake, body weight gain, and blood gasses and mineral concentrations of dairy calves.

Our objective was to examine the effects of two diets with different cation-anion differences on Ca requirements in the growing calf. Holstein calves (n = 48, 24 males) were blocked at 56 to 70 d after birth (80+/-10 kg of body weight) according to sex and birth date and assigned randomly in a 2 x 3 factorial arrangement of dietary treatments containing cation-anion differences as meq (Na + K) - (Cl + S)/kg of diet dry matter and Ca content of 1) 0 and 0.35%, 2) 0 and 0.50%, 3) 0 and 0.65%, 4) 200 and 0.35%, 5) 200 and 0.50%, and 6) 200 and 0.65%. Feed intake and average daily gain did not differ among treatment groups. Plasma pH and Ca were unaffected by dietary Ca content or dietary cation-anion difference. Plasma Cl and P decreased linearly with increasing Ca content in the diet. Plasma HCO3 increased linearly with increased dietary Ca content. Plasma HCO3 and partial pressure of CO2 were higher in calves fed the 200 compared with calves fed the 0 cation-anion difference diets. Plasma Cl was, however, lower in calves fed the 200 compared with calves fed the 0 meq diets. An interaction of Ca content and dietary cation-anion difference was detected for plasma P content. Urinary pH increased linearly with increasing dietary Ca content. Calves fed the 200 meq dietary cation-anion difference had higher urinary pH values than those fed the 0 meq diet. Urinary P excretion was not altered by dietary cation-anion difference or Ca content of the diet. Calves fed the 0 meq diet had higher urinary cocnentrations of Ca and Cl when compared with those fed the 200 meq diet. Bone ash, P, Ca, Mg, and K content of the 10th rib were not affected by dietary treatments. Breaking strength of the seventh and ninth ribs increased quadratically with increasing dietary Ca content. Dietary cation-anion difference had no effect on the breaking strength of the seventh and ninth ribs. Varying the dietary cation-anion difference from 0 to 200 meq/kg of dietary dry matter had no effect on Ca requirement of the growing calf.

Administration of 13-cis-retinoic acid to dairy cattle. 1. Plasma retinoid concentrations and lymphocyte blastogenesis.

Effects of administration of 13-cis-retinoic acid on concentrations in plasma of retinoic acid isomers, retinol, and beta-carotene and on in vitro mitogen-stimulated lymphocyte blastogenesis of peripheral blood mononuclear leukocytes were evaluated in Holstein cattle. Treatments consisted of i.m. injections of 0 (vehicle only), 100, 200, or 400 mg of 13-cis-retinoic acid in dimethylsulfoxide for 7 d. Concentrations of 13-cis- and all-trans-retinoic acids in plasma and in mononuclear leukocytes were elevated in a dose-dependent manner by administration of 13-cis-retinoic acid. Treatment with 13-cis-retinoic acid, however, had no effect on concentrations of retinol and beta-carotene in plasma. In vitro DNA synthesis in unstimulated and mitogen-stimulated mononuclear leukocyte cultures was unaffected by in vivo administration of 13-cis-retinoic acid. In contrast, in vitro supplementation of unstimulated and mitogen-stimulated mononuclear leukocyte cultures with 13-cis-retinoic acid inhibited DNA synthesis relative to unsupplemented cultures. In conclusion, elevated plasma and intracellular concentrations of 13-cis- and all-trans-retinoic acids produced by repeated i.m. administrations of 13-cis-retinoic acid did not affect peripheral blood mononuclear leukocyte function, as measured by the in vitro blastogenic response of peripheral blood lymphocytes.

Dietary marine algae (Schizochytrium sp.) increases concentrations of conjugated linoleic, docosahexaenoic and transvaccenic acids in milk of dairy cows.

Modification of milk fat to contain long-chain (n-3) fatty acids and increased concentrations of conjugated linoleic acid has potential for improving health of consumers. Natural modification of milk through nutritional manipulation of diets for dairy cows is preferable to post-harvest modification. The objectives of this study were to increase the concentrations of beneficial fatty acids in milk fat by feeding a diet rich in (n-3) fatty acids from algae to dairy cows. Cows were fed a control diet, a diet containing algae (Schizochytrium sp.) protected against ruminal biohydrogenation, or a diet containing unprotected algae for 6 wk. Feed intake and milk production were recorded daily. Milk samples were obtained weekly for analysis of milk composition and profile of fatty acids. Percentage of fat in milk of cows fed algae was lower (P < 0.01) than in milk from cows fed the control diet; however, energy-corrected milk production did not differ (P > 0.05). Inclusion of algae in diets decreased (P < 0.01) feed intake. Milk fat from cows fed algae contained greater (P < 0.01) concentrations of conjugated linoleic acid, (n-3) fatty acids (particularly docosahexaenoic acid), and transvaccenic acid. Concentrations of docosahexaenoic acid were greater (P < 0.01) in milk fat from cows fed protected algae compared to milk fat from cows fed unprotected algae. Milk fat from cows fed algae contained lower (P < 0.05) concentrations of total saturated fatty acids compared to cows fed the control diet. In conclusion, milk fat can be modified through nutritional management of dairy cows to provide more favorable fatty acids for consumers.

Influence of supplemental, dietary vitamin A on retinol-binding protein concentrations in the plasma of preruminant calves.

Transport of retinol (vitamin A alcohol) from retinoid stores in the liver to target tissues is accomplished exclusively by a specific plasma protein, retinol-binding protein. Within individuals, retinol-binding protein concentrations in plasma are regulated and remain constant except in extremes of vitamin A nutriture or in disease. In the present study, retinol-binding protein concentrations in plasma from preruminant calves supplemented with 0, 1700 (i.e., current NRC requirement), 34,000, or 68,000 IU of vitamin A daily from birth to 27 d of age (n = 6/treatment) were quantified. Retinol-binding protein concentrations at birth averaged 21 microg/ml (n = 24) or approximately 50% of concentrations in dairy heifers and cows. Plasma retinol and retinol-binding protein concentrations were correlated positively, corroborating the role of vitamin A nutriture in the regulation of retinol-binding protein secretion from the liver. In this regard, dietary vitamin A influenced positively retinol and retinol-binding protein concentrations and, as a consequence, the degree of saturation of retinol-binding protein with retinol. At 27 d of age, calves fed > or = 34,000 IU of vitamin A had substantially higher retinol and retinol-binding protein concentrations than did calves fed < or = 1700 IU of vitamin A, indicating that dietary vitamin A effects positively vitamin A status. The data also suggest that the current NRC requirement may not be sufficient to assure vitamin A adequacy in preruminant calves. Percent saturation of retionol-binding protein with retinol in all calves was < 35%, much lower than anticipated and suggests that the retinol requirement of vitamin A-responsive tissues exceeded vitamin A availability.