Influence of sire plane of nutrition and targeted body weight gain on ewe lamb growth, glucose metabolism, and ovarian reserve.

Abstract

Rambouillet rams were managed on either a positive (POS; gain 12% body weight [BW]; n = 8), maintenance (MAINT; maintain BW; n = 8), or negative (NEG; lose 12% BW; n = 8) plane of nutrition before breeding. Rams were bred to ewes (n = 10 per ram) that were managed similarly throughout gestation, and lambs were fed a common diet postnatally. Two ewe lambs (7.6 ± 0.02 months of age, BW = 47.1 ± 1.17kg) from each sire were selected and within pair, randomly assigned to be managed for a moderate (MOD, 0.11kg/d; n = 23) or accelerated (ACC, 0.20kg/d; n = 22) rate of gain for 56 d. Ewe lamb BW was recorded on a weekly basis and blood was collected on d 0, 28, and 56 for analysis of insulin-like growth factor 1 (IGF-1), triiodothyronine (T3), thyroxine (T4), glucose, blood urea nitrogen (BUN), and non-esterified fatty acids (NEFA). Intravenous glucose tolerance tests (IVGTT) were conducted from d -7 to -4 and d 57 to 64. A unilateral ovariectomy was performed and ovarian follicles were staged and counted macro and microscopically. Sire treatment × day and ewe treatment × day interactions were present for BW (P ≤ 0.05), where POS had slower growth than MAINT and NEG, and tended (P = 0.10) to have reduced average daily gain (ADG) when managed at an accelerated rate of gain.By design, ACC had greater BW and ADG than MOD (P < 0.05). Concentrations of IGF-1 and T4 were greater in ACC than MOD (P ≤ 0.05), and NEG tended to have greater concentrations of IGF-1 than POS and MAINT (P = 0.08). At the first IVGTT, concentration of insulin was influenced by a sire treatment × time interaction (P ≤ 0.05), suggesting impaired secretion in NEG-sires ewes, but no differences in area under the curve (AUC) for glucose, insulin, or their ratio (P ≥ 0.11). No interactive effects of sire and ewe treatment (P ≥ 0.52) were observed at the second IVGTT, but insulin and insulin:glucose ratio were influenced by sire treatment × time (P ≤ 0.02), as NEG had greater insulin concentration at 60min than MAINT (P = 0.03) and greater AUC than POS and MAINT (P ≤ 0.04). No differences in ovary size, weight, or total counts of macro and microscopic follicles were observed (P ≥ 0.23). Ewes fed ACC had a greater number of small surface follicles (P = 0.02), whereas MOD tended to have a greater number of large surface follicles and tertiary follicles (P < 0.06). These findings suggest that paternal plane of nutrition influences female offspring physiology, particularly at varying growth rates.