Blood metabolite profiles in cycling and non-cycling Friesian-Sanga cross-bred cows grazing natural pasture during the post-partum period.

An experiment was conducted to investigate the effect of plasma concentrations of the metabolic hormones [Growth hormone (GH), insulin and insulin-like growth factor -I (IGF-I)] and nutritional metabolites (Glucose, cholesterol, total protein, albumin, globulin, urea and creatinine) on the resumption of post-partum ovarian activity in sixteen Friesian-Sanga cows grazing extensively on native grassland. Blood samples were taken from cows from week 1 to 16 post-partum. Cows were classified as having resumed ovarian activity when a plasma progesterone concentration of ≥ 1.0 ng/ml was recorded for two consecutive weekly samples. Based on the resumption of ovarian activity, cows were classified as early-cycling, late-cycling or non-cycling. The concentrations of the metabolic hormones were measured from week 1 to 10, while those of the nutritional metabolites were measured during week 1, 3, 5, 7 and 9 during the study period. The concentrations of the metabolic hormones, GH and insulin were similar (p > 0.05) in the three ovarian activity groups, likewise the concentrations of the nutritional metabolites, glucose, total protein, globulin, urea and creatinine. Plasma IGF-I concentration was higher (p < 0.001) in early-cycling (18.7 ± 0.74 ng/ml) than in late-cycling (12.4 ± 0.75 ng/ml) and non-cycling (10.4 ± 0.91 ng/ml) cows. Plasma cholesterol concentrations were significantly lower (p < 0.05) in early-cycling (1.94 ± 0.15 mmol/l) compared with late-cycling (2.48 ± 0.12 mmol/l) and non-cycling (2.61 ± 0.11 mmol/l) cows. For plasma albumin concentrations, the levels recorded for early-cycling cows were higher (40.7 ± 2.85 g/l) than in late-cycling (34.4 ± 1.97 g/l) and non-cycling (33.6 ± 2.66) cows. The results suggest that cows with lower plasma concentrations of IGF-I and albumin, but higher plasma cholesterol concentrations were at risk of delayed resumption of post-partum ovarian activity.