B.A. Crooker

Effects of heat stress and plane of nutrition on lactating Holstein cows: I. Production, metabolism, and aspects of circulating somatotropin

Heat stress is detrimental to dairy production and affects numerous variables including feed intake and milk production. It is unclear, however, whether decreased milk yield is primarily due to the associated reduction in feed intake or the cumulative effects of heat stress on feed intake, metabolism, and physiology of dairy cattle. To distinguish between direct (not mediated by feed intake) and indirect (mediated by feed intake) effects of heat stress on physiological and metabolic indices, Holstein cows (n = 6) housed in thermal neutral conditions were pair-fed (PF) to match the nutrient intake of heat-stressed cows (HS; n = 6). All cows were subjected to 2 experimental periods: 1) thermal neutral and ad libitum intake for 9 d (P1) and 2) HS or PF for 9 d (P2). Heat-stress conditions were cyclical with daily temperatures ranging from 29.7 to 39.2 degrees C. During P1 and P2 all cows received i.v. challenges of epinephrine (d 6 of each period), and growth hormone releasing factor (GRF; d 7 of each period), and had circulating somatotropin (ST) profiles characterized (every 15 min for 6 h on d 8 of each period). During P2, HS cows were hyperthermic for the entire day and peak differences in rectal temperatures and respiration rates occurred in the afternoon (38.7 to 40.2 degrees C and 46 to 82 breaths/min, respectively). Heat stress decreased dry matter intake by greater than 35% and, by design, PF cows had similar reduced intakes. Heat stress and PF decreased milk yield, although the pattern and magnitude (40 and 21%, respectively) differed between treatments. The reduction in dry matter intake caused by HS accounted for only approximately 35% of the decrease in milk production. Both HS and PF cows entered into negative energy balance, but only PF cows had increased (approximately 120%) basal nonesterified fatty acid (NEFA) concentrations. Both PF and HS cows had decreased (7%) plasma glucose levels. The NEFA response to epinephrine did not differ between treatments but was increased (greater than 50%) in all cows during P2. During P2, HS (but not PF) cows had a modest reduction (16%) in plasma insulin-like growth factor-I. Neither treatment nor period had an effect on the ST response to GRF and there was little or no treatment effect on mean ST levels or pulsatility characteristics, but both HS and PF cows had reduced mean ST concentrations during P2. In summary, reduced nutrient intake accounted for just 35% of the HS-induced decrease in milk yield, and modest changes in the somatotropic axis may have contributed to a portion of the remainder. Differences in basal NEFA between PF and HS cows suggest a shift in postabsorptive metabolism and nutrient partitioning that may explain the additional reduction in milk yield in cows experiencing a thermal load.

Genome-wide association analysis of thirty one production, health, reproduction and body conformation traits in contemporary U.S. Holstein cows

BackgroundGenome-wide association analysis is a powerful tool for annotating phenotypic effects on the genome and knowledge of genes and chromosomal regions associated with dairy phenotypes is useful for genome and gene-based selection. Here, we report results of a genome-wide analysis of predicted transmitting ability (PTA) of 31 production, health, reproduction and body conformation traits in contemporary Holstein cows.ResultsGenome-wide association analysis identified a number of candidate genes and chromosome regions associated with 31 dairy traits in contemporary U.S. Holstein cows. Highly significant genes and chromosome regions include: BTA13s GNAS region for milk, fat and protein yields; BTA7s INSR region and BTAXs LOC520057 and GRIA3 for daughter pregnancy rate, somatic cell score and productive life; BTA2s LRP1B for somatic cell score; BTA14s DGAT1-NIBP region for fat percentage; BTA1s FKBP2 for protein yields and percentage, BTA26s MGMT and BTA6s PDGFRA for protein percentage; BTA18s 53.9-58.7 Mb region for service-sire and daughter calving ease and service-sire stillbirth; BTA18s PGLYRP1-IGFL1 region for a large number of traits; BTA18s LOC787057 for service-sire stillbirth and daughter calving ease; BTA15s CD82, BTA23s DST and the MOCS1-LRFN2 region for daughter stillbirth; and BTAXs LOC520057 and GRIA3 for daughter pregnancy rate. For body conformation traits, BTA11, BTAX, BTA10, BTA5, and BTA26 had the largest concentrations of SNP effects, and PHKA2 of BTAX and REN of BTA16 had the most significant effects for body size traits. For body shape traits, BTAX, BTA19 and BTA3 were most significant. Udder traits were affected by BTA16, BTA22, BTAX, BTA2, BTA10, BTA11, BTA20, BTA22 and BTA25, teat traits were affected by BTA6, BTA7, BTA9, BTA16, BTA11, BTA26 and BTA17, and feet/legs traits were affected by BTA11, BTA13, BTA18, BTA20, and BTA26.ConclusionsGenome-wide association analysis identified a number of genes and chromosome regions associated with 31 production, health, reproduction and body conformation traits in contemporary Holstein cows. The results provide useful information for annotating phenotypic effects on the dairy genome and for building consensus of dairy QTL effects.

Effect of Artificial Selection on Runs of Homozygosity in U.S. Holstein Cattle

The intensive selection programs for milk made possible by mass artificial insemination increased the similarity among the genomes of North American (NA) Holsteins tremendously since the 1960s. This migration of elite alleles has caused certain regions of the genome to have runs of homozygosity (ROH) occasionally spanning millions of continuous base pairs at a specific locus. In this study, genome signatures of artificial selection in NA Holsteins born between 1953 and 2008 were identified by comparing changes in ROH between three distinct groups under different selective pressure for milk production. The ROH regions were also used to estimate the inbreeding coefficients. The comparisons of genomic autozygosity between groups selected or unselected since 1964 for milk production revealed significant differences with respect to overall ROH frequency and distribution. These results indicate selection has increased overall autozygosity across the genome, whereas the autozygosity in an unselected line has not changed significantly across most of the chromosomes. In addition, ROH distribution was more variable across the genomes of selected animals in comparison to a more even ROH distribution for unselected animals. Further analysis of genome-wide autozygosity changes and the association between traits and haplotypes identified more than 40 genomic regions under selection on several chromosomes (Chr) including Chr 2, 7, 16 and 20. Many of these selection signatures corresponded to quantitative trait loci for milk, fat, and protein yield previously found in contemporary Holsteins.

Effects of heat stress and nutrition on lactating Holstein cows: II. Aspects of hepatic growth hormone responsiveness.

Heat stress (HS) is a multibillion-dollar problem for the global dairy industry, and reduced milk yield is the primary contributor to this annual economic loss. Feed intake declines precipitously during HS but accounts for only about 35% of the decreased milk synthesis, indicating that the physiological mechanisms responsible for decreased milk production during HS are only partly understood. Thus, our experimental objectives were to characterize the direct effects of HS on the somatotropic axis, a primary regulator of metabolism and milk yield. We recently reported no differences in mean growth hormone (GH) concentrations, GH pulsatility characteristics, or GH response to growth hormone releasing factor in HS versus pair-fed (PF) thermoneutral controls. Despite similarities in circulating GH characteristics, plasma insulin-like growth factor (IGF)-I concentrations were reduced during heat stress conditions but not in PF animals, suggesting that uncoupling of the hepatic GH-IGF axis may occur during HS. We investigated this possibility by measuring proximal indicators of hepatic GH signaling following a GH bolus. Heat stress but not PF decreased abundance of the GH receptor and GH-dependent signal transducer and activator of transcription (STAT)-5 phosphorylation. Consistent with reduced GH signaling through STAT-5, basal hepatic IGF-I mRNA abundance was lower in HS cows. Thus, the reduced hepatic GH responsiveness (in terms of IGF-I gene expression) observed during HS appears to involve mechanisms at least partially independent of reduced nutrient intake. The physiological significance of reduced hepatic GH receptor abundance during HS is unclear at this time. Aside from reducing IGF-I production, it may reduce other GH-sensitive bioenergetic processes such as gluconeogenesis.

Hepatic gene expression in multiparous Holstein cows treated with bovine somatotropin and fed n-3 fatty acids in early lactation.

Multiparous cows were fed supplemental dietary fat and treated with bST to assess effects of n-3 fatty acid supply, bovine somatotropin (bST), and stage of lactation on hepatic gene expression. Cows were blocked by expected calving date and previous milk yield and assigned randomly to treatment. Supplemental dietary fat was provided from calving as either whole high-oil sunflower seeds (SS; 10% of dietary dry matter; n-6/n-3 ratio of 4.6) as a source of linoleic acid or a mixture of Alifet-High Energy and Alifet-Repro (AF; 3.5 and 1.5% of dietary dry matter, respectively; n-6/n-3 ratio of 2.6) as a source of protected n-3 fatty acids. Cows were treated with 0 (SSN, AFN) or 500 (SSY, AFY) mg of bST every 10 d from 12 to 70 d in milk (DIM) and at 14-d intervals thereafter. Liver biopsies were collected on -12, 10, 24, and 136 DIM for gene expression analysis. Growth hormone receptor (GHR), insulin-like growth factor-I (IGF-I), IGF-binding protein-3 (IGFBP3), hepatic nuclear factor 4alpha (HNF4alpha), fibroblast growth factor-21 (FGF-21), and peroxisome proliferator-activated receptor alpha (PPARalpha) were the target genes and hypoxanthine phosphoribosyltransferase (HPRT) was used as an endogenous control gene. Expression was measured by quantitative real-time reverse transcription-PCR analyses of 4 samples from each of 32 cows (8 complete blocks). Amounts of hepatic HPRT mRNA were not affected by bST or diet but were increased by approximately 3.8% in early lactation (3.42, 3.52, 3.54, and 3.41 x 10(4) message copies for -12, 10, 24, and 136 DIM, respectively). This small change had little detectable impact on the ability of HPRT to serve as an internal control gene. Amounts of hepatic GHR, IGF-I, and IGFBP3 mRNA were reduced by 1.5 to 2-fold after calving. Expression of GHR and IGF-I increased and IGFBP3 tended to increase within 12 d (by 24 DIM) of bST administration. These effects of bST persisted through 136 DIM. Hepatic HNF4alpha mRNA was not altered by DIM or any of the treatments. Abundance of PPARalpha mRNA was unchanged through 24 DIM but increased by 136 DIM. There was a trend for an interaction of bST, diet, and DIM on PPARalpha mRNA abundance from 24 to 136 DIM because the amount of PPARalpha mRNA increased in SSN, SSY, and AFN cows but was not altered in AFY cows. The amount of FGF-21 mRNA increased markedly in early lactation but, like HNF4alpha mRNA, was not affected by bST, diet, or their interactions. These results indicate 1) that bST induced increases in hepatic expression of GHR, IGF-I, and IGFBP3 when cows were in negative energy balance in early lactation, 2) there was no effect of reduced dietary n-6/n-3 content on hepatic gene expression, and 3) there was support for a potential homeorhetic role of hepatic FGF-21 via uncoupling the somatotropin-IGF-axis in early lactation.

Association of somatotropin (BST) gene polymorphism at the 5th exon with selection for milk yield in holstein cows

A selection project produced control cows from continuous matings with breed average bulls for predicted transmitting ability for milk (PTA-milk) in 1964 and select cows from matings to four of the highest PTA-milk bulls each year since 1964. Blood samples were collected in 1992 when milk yield difference of select and control line cows exceeded 3,800 kg of milk/305-day lactation. Genomic DNA from control (n = 49) and select (n = 101) cows was analyzed for the presence of variants associated with amino acid position 127 (leucine, AluI[+]; valine, AluI[-]) of bovine somatotropin (bST). Amplification of a 428 base-pair fragment of the bST gene from individual cows, subsequent restriction enzyme (AluI) digestion, and separation resulting fragments indicated three genotypes AluI(+/+), AluI(+/-), and AluI(-/-) in 110, 39, and 1 animal(s), respectively. Gene frequencies of leucine127 and valine 127 alleles were similar for control (0.867m 0.133) and select (0.861, 0.139) animals. United States Department of Agriculture-PTA values were compared between the two genotypes, AluI(+/+) and AluI(+/-). Estimated breeding value for milk (EBV-milk) and average yield deviation for milk (AYD-milk) were not associated with genotype for control animals. However, presence of the valine allele was correlated with decreased EBV-milk (P = 0.03) and AYD-milk (P = 0.16) in select animals and accounted for a decrease of approximately 170 kg of EBV-milk and 240 kg of AYD-milk.

Metabolic connections between nutrient intake and lactational performance in the sow

Abstract Improvement in the efficiency of milk synthesis in the sow can be accomplished only with a thorough understanding of the metabolic mechanisms relating nutrient intake to lactational performance. We have begun to describe these connections systematically and quantitatively through mathematical modelling. Our model is an integration of our present knowledge base with concepts of lactating sow metabolism. It is limited by serious inadequacy of present information, but it has guided us to ask key questions which can be investigated by animal experimentation. We are presently studying the metabolism of lipids in adipose tissue, and the impacts of lysine and amino acid intake on metabolic state and lactational performance, to elucidate aspects of the connection between nutrient intake and lactational performance. The pressing need for more information at several levels of biological organization is described. Collaboration among scientists across disciplines can increase the productivity and efficiency of both scientific and practical endeavours. It is imperative that publication of research results include thorough descriptions of animals, diets and environments to allow better interpretation and use of results.

Effect of sample stratification on dairy GWAS results

BackgroundArtificial insemination and genetic selection are major factors contributing to population stratification in dairy cattle. In this study, we analyzed the effect of sample stratification and the effect of stratification correction on results of a dairy genome-wide association study (GWAS). Three methods for stratification correction were used: the efficient mixed-model association expedited (EMMAX) method accounting for correlation among all individuals, a generalized least squares (GLS) method based on half-sib intraclass correlation, and a principal component analysis (PCA) approach.ResultsHistorical pedigree data revealed that the 1,654 contemporary cows in the GWAS were all related when traced through approximately 10–15 generations of ancestors. Genome and phenotype stratifications had a striking overlap with the half-sib structure. A large elite half-sib family of cows contributed to the detection of favorable alleles that had low frequencies in the general population and high frequencies in the elite cows and contributed to the detection of X chromosome effects. All three methods for stratification correction reduced the number of significant effects. EMMAX method had the most severe reduction in the number of significant effects, and the PCA method using 20 principal components and GLS had similar significance levels. Removal of the elite cows from the analysis without using stratification correction removed many effects that were also removed by the three methods for stratification correction, indicating that stratification correction could have removed some true effects due to the elite cows. SNP effects with good consensus between different methods and effect size distributions from USDA’s Holstein genomic evaluation included the DGAT1-NIBP region of BTA14 for production traits, a SNP 45kb upstream from PIGY on BTA6 and two SNPs in NIBP on BTA14 for protein percentage. However, most of these consensus effects had similar frequencies in the elite and average cows.ConclusionsGenetic selection and extensive use of artificial insemination contributed to overlapped genome, pedigree and phenotype stratifications. The presence of an elite cluster of cows was related to the detection of rare favorable alleles that had high frequencies in the elite cluster and low frequencies in the remaining cows. Methods for stratification correction could have removed some true effects associated with genetic selection.

Effect of continuous milking and prostaglandin E2 on milk production and mammary epithelial cell turnover, ultrastructure, and gene expression

Mammary epithelial cell (MEC) growth is reduced in continuously milked (CM) mammary glands, and administration of a mammogenic compound such as prostaglandin E(2) (PGE(2)) at parturition might improve MEC growth in CM tissue. The objectives were to 1) compare MEC turnover, ultrastructure, and gene expression in CM and involuting mammary tissue, and 2) evaluate the effects of CM and intramammary infusion of PGE(2) on early lactation MEC turnover, ultrastructure, mammary gene expression, milk yield, and composition. First- and second-lactation cows (n = 8) were used in a half-udder model, in which one-half was dry for 60 d (CTL) and the other was CM. Udder halves (n = 16) were assigned to a postpartum (PP) treatment of PGE(2) (+PGE(2); 875 mug/10 mL of medium-chain triglyceride oil) or no PGE(2) (-PGE(2)) treatment at parturition and at 72 h PP. Biopsies of CM and CTL quarters were obtained during milk stasis (MS) of the CTL half at 3 and 7 d after dry-off of the CTL half (3d-MS; 7d-MS) and postpartum (PP) at 2 and 4 d (2d-PP; 4d-PP). Milk yield was reduced (P < 0.01) in CM udder halves compared with CTL halves (13.2 vs. 22.1 kg/d), but reductions were less in second-lactation cows. The apoptotic index was greater (P < 0.05) in CTL glands than in CM glands (3d-MS, 0.52 vs. 0.11% and 7d-MS, 0.24 vs. 0.12, respectively). Proliferation of MEC was unchanged at 3d-MS, but was increased (P = 0.01) in CTL halves at 7d-MS compared with CM halves (3.10 vs. 0.93%). At 2d-PP, MEC proliferation was increased (P = 0.05) in CM halves compared with CTL halves (1.3 vs. 0.6%), but was unaffected by PGE(2) (P > 0.2). Apoptosis was elevated in early lactation regardless of treatment. Ultrastructure was unchanged by dry period length or PGE(2). In prepartum tissue, involution in CTL halves increased (P < 0.05) the expression of the proapoptotic genes Bcl-2-associated x protein (bax) and IGFBP5 and decreased (P < 0.05) alpha-lactalbumin expression compared with CM tissue. In PP mammary tissue, CTL halves expressed greater (P < 0.05) levels of ATP-binding cassette 1 (ABC1) and IGFBP5. Treatment with PGE(2) did not alter (P > 0.1) gene expression. The results confirm that CM reduced milk yield of cows with a mammary growth requirement. Reduced MEC turnover and milk yield were not alleviated by IMI of PGE(2), which indicates that peripartum PGE(2) concentrations in CM glands are not limiting mammary growth or milk synthesis.

Administration of Bovine Somatotropin in Early Lactation: A Meta-Analysis of Production Responses by Multiparous Holstein Cows

A meta-analysis was conducted to assess production responses before 90 d in milk (DIM) when bovine somatotropin (bST) administration was initiated between 5 and 35 DIM. The database was developed from 13 studies of multiparous cows that were published between 1985 and 2006 and from an unpublished study that complied with the study selection criteria. The database included results from 842 cows and provided 50 treatment means for the effect of bST on 3.5% fat-corrected milk (FCM) in early lactation. Effects of bST were investigated using mixed model procedures that included fixed (intercept and slope) and random (intercept and slope) effects for independent variables. Yields of milk (38.6 +/- 1.3 kg/d) and FCM (37.6 +/- 1.6 kg/d) by control cows before 90 DIM were increased by 2.6 +/- 0.8 and 3.2 +/- 0.6 kg/d by bST administration. Fat content in milk from bST-treated cows was 0.31 +/- 0.10 percentage units greater than that from control cows (3.46 +/- 0.13%) but milk protein content (2.95 +/- 0.03%) was not altered by bST. Milk fat (1.39 +/- 0.10 kg/d) and protein (1.15 +/- 0.04 kg/d) yields by controls were increased 0.16 +/- 0.03 and 0.07 +/- 0.03 kg/d by bST, respectively. Dry matter intake and body weight loss were not altered by bST before 90 DIM, but duration of negative energy balance was prolonged and overall energy balance during this interval reduced when cows were treated with bST. Results are consistent with the premise that bST-treated cows partition nutrients and energy toward milk synthesis for a longer duration and thus likely need a longer interval to replenish their body reserves than cows not treated with bST. Production responses to bST were not altered when cows consumed typical early-lactation diets supplemented with fat except that supplemental fat tended to decrease the magnitude of the effect of bST on milk fat content and decreased the effect of bST on fat and protein yield. Yield of FCM increased curvilinearly with the amount of bST administered. Results indicate that initiation of bST administration to cows before 35 DIM increased FCM yield but the response was at the low end of that typically observed when bST administration is initiated in wk 9 of lactation.