G.L. Lindberg

The effect of mitochondrial DNA on milk production and health of dairy cattle

Maternal lineage effects, probably indicative of mitochondrial DNA (mtDNA) differences, may be important for milk production and reproductive success in dairy cattle (Bos taurus). Sequence variation of mtDNA in 36 maternal lineages of dairy cattle was studied with animal models to assess effects on milk production and reproductive traits. Cattle within maternal lineages defined by registered pedigrees were assumed to be uniform for the nucleotide sequences examined. Sequence polymorphisms of bovine mtDNA were shown to be associated with milk production, reproduction, and health costs incurred. One particular base-pair substitution was associated with additional production of 842 kg milk and 37 kg milk fat per cow per lactation. Another single base-pair substitution was associated with a decrease of 36 days and one unsuccessful breeding between successive calvings. Effects of this size are economically important and have broad implications in genetic selection of dairy cattle.

Short Communication : Estimates of Genetic Variation of Milk Fatty Acids in US Holstein Cows

Interest in changing the milk fatty acid profile is growing. However, little is known about the genetic variability of milk fatty acids in the US Holstein population. Therefore, genetic parameters for milk fatty acids were estimated using a single-trait, mixed, linear animal model on 592 individual milk samples from 233 daughters of 53 sires in a cow herd genetically representative of the US Holstein population. Heritability (h(2)) and repeatability (r) estimates +/- standard errors for yields of individual fatty acids ranged from 0.00 +/- 0.08 (C4:0) to 0.43 +/- 0.13 (C12:0) for heritabilities and from 0.21 +/- 0.05 (C18:1) to 0.43 +/- 0.05 (C12:0) for repeatabilities. Saturated (h(2) = 0.23 +/- 0.12; r = 0.36 +/- 0.05) and de novo synthesized fatty acids (C6:0 to C14:0; h(2) = 0.30 +/- 0.13; r = 0.40 +/- 0.05) had numerically higher estimates than did monounsaturated (h(2) = 0.09 +/- 0.09; r = 0.22 +/- 0.05) and polyunsaturated fatty acids (h(2) = 0.08 +/- 0.09; r = 0.27 +/- 0.05). For relative proportions of individual fatty acids, the greatest heritability and repeatability estimates were obtained for C8:0 (h(2) = 0.18 +/- 0.12; r = 0.36 +/- 0.05), C10:0 (h(2) = 0.22 +/- 0.13; r = 0.46 +/- 0.05), C12:0 (h(2) = 0.18 +/- 0.12; r = 0.46 +/- 0.05), C16:0 (h(2) = 0.09 +/- 0.12; r = 0.48 +/- 0.05), C16:1 (h(2) = 0.49 +/- 0.13; r = 0.49 +/- 0.05), and C18:0 (h(2) = 0.24 +/- 0.11; r = 0.39 +/- 0.05). Our results suggest the existence of genetic variability of milk fatty acids, in particular of medium-and long-chain fatty acids (C8:0 to C18:0), which could be used to improve the nutritional and textural properties of milk fat by selective breeding.

Associations among individual proteins and fatty acids in bovine milk as determined by correlations and factor analyses

Associations among quantities and concentrations of individual milk proteins and fatty acids were determined in individual milk samples from 233 Holstein cows. Correlation coefficients among the six major proteins and the eleven major fatty acids in bovine milk were grouped hierarchically. Factor analyses grouped the milk components into seven families: fatty acids 4:0-6:0, 6:0-16:0, 16:0, 18:0, 16:1 plus 18:1 plus 18:2, all milk proteins and beta-lactoglobulin alone. Correlation coefficients and groupings by factor analyses coincided with shared pathways of synthesis or genetic origins of milk proteins and fatty acids because they are the basis of the correlation coefficients. Hence, the results from correlations and factor analyses could be used to develop hypotheses for the synthesis of milk components and other coordinately regulated physiological processes.

Effects of lipid supplementation on the yield and composition of milk from cows with different β-lactoglobulin phenotypes

Responses to lipid supplementation differ between dairy breeds and genetic lines suggesting nutrition by genotype interactions. beta-Lactoglobulin phenotype is associated with changes in yield and composition of milk. The response of cows with different beta-lactoglobulin phenotypes to lipid supplementation has not been examined. Furthermore, we examined whether lipid supplementation alters milk protein composition. By using a randomized block design, we fed Holstein cows for 3 wk either a control diet containing 2.8% crude fat (n = 19) or an experimental diet that was supplemented with 4.2% tallow (n = 20). Before randomization, all cows were fed the supplemental tallow diet for at least 2 wk. Dry matter intake, body weight, milk yield, and milk composition were measured in the last week before and during the experimental period. Feeding supplemental tallow increased dry matter intake and yields of milk and milk components, including casein content, without decreasing milk component content or altering milk protein composition. On the low-fat control diet, cows with the beta-lactoglobulin allele B had a greater milk and milk component yield than cows with the A allele, whereas no differences by beta-lactoglobulin phenotype were observed in cows on the tallow supplement diet. Our results suggest that cows that differ in beta-lactoglobulin phenotype respond differently to a low-fat diet and that feeding cows 4.2% of additional tallow increases milk yield without affecting milk component content and milk protein composition.

Sequence heteroplasmy of D-loop and rRNA coding regions in mitochondrial DNA from Holstein cows of independent maternal lineages.

A mitochondrial DNA (mtDNA) fragment containing the D-loop, phenylalanine tRNA, valine tRNA, and 12S and 16 rRNA genes was cloned and sequenced from 36 cows of 18 maternal lineages to identify the polymorphic sites within those regions and to detect the existence of heteroplasmic mtDNA in cows. Seventeen variable sites were observed within the D-loop and rRNA coding regions of bovine mtDNA within a 2.5-kb span. The hypervariable sites in the D-loop and rRNA coding regions were identified at nucleotide positions 169, 216, and 1594. Heteroplasmic mtDNA (variable mtDNA within a tissue) existed extensively in cows and was detected within the above regions in 11 of 36 cows sequenced. The insertion, deletion, and nucleotide transversion polymorphisms were found only in homopolymer regions. Heteroplasmy was observed frequently and seemingly is persistent in cattle. Though heteroplasmy was demonstrated, most lineages and mtDNA sites showed no heteroplasmy.

Intrinsic labeling of bovine milk with enriched stable isotopes of zinc.

Abstract Bovine milk was labeled intrinsically with enriched stable isotopic zinc for human bioavailability studies. Intrajugular administration of zinc isotopes temporarily increased the plasma zinc concentration of Ayrshire cows by as much as 76%, but milk zinc concentration and the distribution of zinc between casein and whey did not change appreciably. Milk zinc isotopic enrichment reached 105 and 613 atom % excess for 67Zn and 70Zn, respectively within 4-12 hr of zinc administration and decreased gradually over several days. This degree of isotopic enrichment is sufficient for testing bioavailability to infants of intrinsic zinc from milk-based formulas.

Effects of glucagon infusions on protein and amino acid composition of milk from dairy cows

Changing the composition of milk proteins and AA affects the nutritional and physical properties of dairy products. Intravenous infusions of glucagon decreases milk protein production and concentration by promoting the use of gluconeogenic blood AA for hepatic glucose synthesis. Little is known about how the diversion of AA to gluconeogenesis affects the composition of milk proteins and AA. The objective was to quantify changes in composition of milk protein and AA in response to i.v. glucagon infusions. Three separate experiments were used: 1) 8 Holstein cows were fed ad libitum and infused with glucagon at 10 mg/d for 14 d, 2) 7 Holstein cows were feed restricted and infused with glucagon at 10 mg/d for 14 d, and 3) 4 Brown Swiss cows were infused with glucagon at 5 and 10 mg/d for 2 d each. Milk and milk component yields and milk protein and amino acid composition of samples, collected with blood samples at the first and last day of the glucagon infusion period, were compared with those collected 1 d before and after the glucagon infusion period. Glucagon infusions decreased milk protein production and concentration in each experiment by at least 0.2 +/- 0.05 kg/d and 4 +/- 0.4 g/L, respectively. The decrease was accompanied by changes in milk protein composition, the most consistent being an increase in kappa-casein (1.68 +/- 0.27%). Overall, glucagon infusions resulted in higher proportions of kappa-casein and alpha(S2)-casein (1.34 +/- 0.51%) and smaller proportions of alpha(S1)-casein (-3.83 +/- 1.75%) and alpha-lactalbumin (-0.91 +/- 0.32%). Glucagon had little impact on milk AA composition except an increase in glycine (0.26 +/- 0.11%). The results suggest that milk protein synthesis is regulated by many factors including AA and glucose availability.