Dietary fat effects on rumen fermentation, milk production, and reproduction, and economic implications for dairy production

The purpose of the current investigations was to examine the effects of supplemental dietary fat on interactions with rumen microbes and subsequent fermentation products in vitro, and milk production and reproduction in vivo of early lactation dairy cows. The in vivo experiment also included recombinant bovine somatotropin (bST) at a dose of 208 mg/14 days to study its potential use to stimulate reproductive endocrine responses and improve pregnancy rate early postpartum.; In vitro experiments utilized six fat sources, whole cottonseed (WCS), tallow, Menhaden fish oil, poultry fat, calcium soap of poultry fat, and corn oil. Fat sources were mixed with hominy, corn silage, or alfalfa hay before components were mixed and incubated with rumen bacteria for 0, 12, 24, 48 and 96 h. Neutral detergent fiber remaining in samples did not differ between treatments, indicating that dietary fat in this experiment did not inhibit fiber digestibility.; In vivo experiment utilized WCS and bST in a 2 x 2 factorial design. Treatments were 0% WCS, 0 bST (T0), 15% of diet dry matter (DM) WCS, 0 bST (T1), 0% WCS, 208 mg/14 d bST (T2), and 15% WCS plus 208 mg/14 d bST. Primi- and multiparous cows (n = 186) were assigned randomly to treatments. Milk production was increased by WCS (35.09 vs. 34.46 kg; p < 0.001), as was milk fat percentage (3.45 vs. 3.15%; p < 0.0001). Whole cottonseed increased plasma high density lipoprotein (HDL) cholesterol (p < 0.001), and progesterone (P₄; P < 0.001). Plasma HDL was also increased by bST (p < 0.001). First lactation animals which calved during the warm months of the trial had 40% greater pregnancy rates to two timed artificial inseminations when receiving bST (p = 0.0216).; Finally, a linear program was constructed of an existing dairy farm to model the potential financial impact of research efforts in nutrition and reproduction on the farm enterprise. Ration balancing and whole farm nitrogen and phosphorus balancing were included as elements of the program. The model selected WCS at the maximum allowed level to meet energy and protein requirements. The model also selected bST as an alternative technology to increase animal productivity.