Pregnancy, Bovine Somatotropin, and Dietary n-3 Fatty Acids in Lactating Dairy Cows: I. Ovarian, Conceptus, and Growth Hormone–Insulin-Like Growth Factor System Responses

Regression analysis (third-order curves) of daily milk production starting 10 DIM until the start of bST treatment and timed AI for cows fed either 0 (least squares means: ■) or 1.9% (least squares means:□) calcium salt of fish oil-enriched lipid diets. Pattern of regression curves differed (P<0.01). Regression equations: 1.9% Fish Oil: ŷ = 13.12 + 0.923x−0.0117x² + 0.000045x³; 0% Fish Oil: ŷ = 16.51 + 0.808x−0.0137x² + 0.000085x³, ; where ŷ = milk production and x = DIM.

Linear regression of plasma insulin concentrations for cows fed fish oil-enriched lipid (FO) at 0 (least squares means: ■) or 1.9% (least squares means: □) of dietary DM from 14 to 53 DIM. Feeding FO decreased (P<0.01) plasma insulin concentrations compared with control cows in relation to DIM. Regression equations: 0% Fish Oil: ŷ = 0.56 + 0.011x; 1.9% Fish Oil: ŷ = 0.75 + 0.0012x, ; where ŷ = insulin concentration and x = DIM.

Regression analysis (second-order curves) of daily milk production from d 0 to 17 of a synchronized estrous cycle (d 0) for cyclic and pregnant cows fed the control diet and injected with bST (least squares means:□) or not (least squares means: ■) on d 0 and 11. Pattern of regression curves differed (P<0.01). Regression equation: bST: ŷ = 33.30−0.125x−0.0029x²; no bST: ŷ = 37.05 + 0.281x −0.0118x²; ŷ = milk production and x = days after GnRH (estrus).

Concentrations of plasma progesterone of cyclic and pregnant cows not given bST (n = 10; □) and those given bST (n = 11; ▴) collected from d 0 to 17 of a synchronized estrous cycle differed (P<0.05). All cows were fed the control diet. Concentrations of progesterone at days designated differed: *P<0.10; **P<0.05.

Profiles of plasma growth hormone (GH) concentrations of cyclic cows fed control diet (no bST; △), cyclic cows fed control diet with bST injections (▴), cyclic cows fed FO (---×---), cyclic cows fed FO with bST injections (---○---), pregnant cows fed control diet (no bST; □), and pregnant cows fed control diet with bST injections (■) from d 0 to 17 of a synchronized estrous cycle. All 3 groups of cows given bST had greater mean GH concentrations than cows not injected with bST (P<0.01). Of those given bST, cows fed FO and pregnant cows had greater (P<0.05) mean GH concentrations than cyclic cows fed the control diet. Pooled standard errors for bST-treated cows = 3.31 and non-bST-treated cows = 1.13.

Profiles of plasma IGF-I concentrations of cyclic cows fed control diet (no bST; △), cyclic cows fed control diet with bST injections (▴), cyclic cows fed FO (---×---), cyclic cows fed FO with bST injections (---○---), pregnant cows fed control diet (no bST; □), and pregnant cows fed control diet with bST injections (■) from d 0 to 17 of a synchronized estrous cycle. All 3 groups of cows given bST had greater (P<0.01) mean IGF-I concentrations than cows not injected with bST. The FO-fed cows injected with bST had lower (P<0.05) IGF-I plasma concentrations and pregnant cows injected with bST had greater (P<0.05) IGF-I plasma concentrations than cyclic cows fed the control diet with bST injections as detected by homogeneity of regression. Pooled standard errors for bST-treated cows = 29.9 and non-bST-treated cows = 22.2.