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.
