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.