Influence of Blood Metabolite Concentrations on the Resumption of Postpartum Ovarian Function in Friesian-Sanga Crossbred Cows

Abstract

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 (IGFI)] and nutritional metabolites (glucose, cholesterol, total protein, albumin, globulin, urea and creatinine) on the resumption of postpartum ovarian activity in sixteen Friesian-Sanga crossbred cows at the Animal Research Institute’s Frafraha station. Also, correlation among the metabolic hormones and the nutritional metabolites were assessed. The cows grazed extensively on natural grassland without any feed supplementation. They were weighed monthly and scored for body condition once every week using the 9-point score (1= very thin to 9 = obese). Blood samples were taken from cows from week 1 to 16 postpartum and processed for plasma. The concentrations of the metabolic hormones (GH, insulin and IGF-I in the plasma) were measured weekly from week 1 to 10 postpartum, whilst the nutritional metabolites (glucose, cholesterol, total protein, albumin, globulin, urea and creatinine) were determined at two-weekly intervals (weeks 1, 3, 5, 7 and 9). Resumption of postpartum ovarian cyclicity was determined by measuring progesterone concentration in the plasma from week 1 to 16 in the cows. 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. Results from the present study indicate that 37.5% of cows commenced ovarian cyclicity early (by 56 days postpartum), 37.5 % commenced ovarian activity late (within 57-112 days postpartum), while 25 % failed to commence ovarian cyclicity by 112 days (16 weeks) postpartum. Partial milk yield, body condition score or body weight was not significantly different (P>0.05) in the three ovarian activity groups. 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 concentration was 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 g/L) cows. There was a positive correlation between IGF-I and insulin (r = 0.328; P<0.01); glucose (r = 0.260; P<0.05), and cholesterol (r = 0.262; P<0.05), while insulin was positively correlated with glucose (r = 0.502; P<0.10). Glucose was negatively correlated with cholesterol (r = - 0.264; P<0.05), and globulin (r= -0.323; P<0.01); but positively correlated with albumin (r = 0.291; P<0.05). Total protein was positively correlated with globulin (r = 0.706; P<0.01), and urea (r = 0.442; P<0.01). Albumin was negatively correlated with globulin (r = -0.654; P<0.01), and globulin was positively correlated with urea (r = 0.267; P<0.05). The results from the study suggest poor nutritional and metabolic status of cows. Higher plasma concentrations of IGF-I in the early postpartum period was associated with early resumption of ovarian cyclicity in cows. Also, cows with lower plasma concentrations of albumin, but higher plasma concentrations of cholesterol were at risk of delayed resumption of postpartum ovarian activity. Introducing feed supplementation strategies during the postpartum period should positively influence the synthesis and secretion of metabolic hormones associated with resumption of ovarian cyclicity and improve the reproductive performance of the Friesian-Sanga crossbred cows.