Comparison of metabolites and hormones involved in the control of energy partitioning during the lactation of dairy ewes and goats.

This research studied the evolution of metabolites and hormones involved in the control of energy partitioning during early and midlactation of dairy ewes and goats and assessed in mid-lactation possible interactions with the type of carbohydrates used in the diet. Twenty Sarda ewes and 20 Saanen goats were compared from 15 ± 5 d in milk (DIM; mean ± st.dev.) to 134 ± 5 DIM in the same feeding conditions. Since parturition, each species was fed a high starch diet (20.4% starch, 35.5% NDF, DM basis), whereas from 92 ± 11 DIM each species was allocated to 2 dietary treatments: high starch (HS; 20.0% starch, 36.7% NDF, DM basis) and low starch-high digestible fiber (LS: 7.8% starch, 48.8% NDF, DM basis) diets. The LS diet was obtained by substituting cereal grains with soyhulls. Blood samples were collected monthly and analyzed for plasma glucose, NEFA, growth hormone (GH), IGF-1 and leptin. Data were studied by using the PROC MIXED procedure of SAS for repeated measurements. From early to mid-lactation, glucose concentration was higher in ewes than in goats (54.6 vs. 48.4 mg/dl ± 1.2 (mean+SEM); P < 0.0001). NEFA concentration was lower in ewes than in goats (0.25 vs. 0.31 mmol/L ± 0.03; P = 0.036). IGF-1 concentration did not differ (108.8 vs. 94.2 ng/mL ± 11.64; P > 0.1). Goats had higher plasma GH (4.47 vs. 2.28 ng/mL ± 0.57; P < 0.001), with a marked peak in early lactation not observed in ewes, higher leptin concentration (26.3 vs. 11.4 ng/ml ± 2.1; P < 0.0002), and lower plasma insulin content (0.11 vs. 0.26 μg/L ± 0.02; P < 0.0001) than the ewes. In mid-lactation, metabolites and hormones were not affected by the diets in both species. In conclusion, this experiment found that (1) the ewes had a hormonal profile more directed to the partitioning of dietary energy in favor of body reserve accumulation, rather to milk production, than the goats; (2) in mid lactation the hormonal status was not affected by the prevalent type of carbohydrate (starch or digestible fiber) of the diets; iii) blood leptin was much higher in goats than in ewes, despite the latter accumulated much more body reserves than the former.