Nutritional and metabolic modulation of the male effect on the resumption of ovulatory activity in goats

Abstract

The present study evaluated possible modulation of the buck effect by nutritional and metabolic cues during the transition to the breeding season in adult goats with divergent bodyweight (BW) and body condition (BCS) at 27°N. In mid-February, goats (Boer × Spanish, n = 32) were assigned to receive one of the following two experimental diets to fulfill different allowances of nutritional requirements: (1) 100% (n = 16; BW = 52.3 ± 1.5 kg, BCS = 1.6 ± 0.1 units; T-100) or (2) 150% (n = 16; BW = 60.9 ± 2.4 kg, BCS = 1.6 ± 0.1 units; T-150) from February to August. Blood samples were collected to analyse thyroxine (T4), triiodothyronine (T3), non-esterified fatty acids (NEFA), triglycerides (Tg) and progesterone (P4). Final BW and BCS favoured (P < 0.001) the T-150 group (74.9 ± 2.8 v. 56.3 ± 1.4 kg, and 4.4 ± 0.2 v. 1.9 ± 0.1 units, respectively). However, mean values for NEFA, Tg, T3 and T4 did not differ (P > 0.05) between the experimental groups. Thereafter, in early August, half of the does in each diet treatment were randomly selected for determining the response to the ‘male effect’ (WM), forming the following two treatment groups: (1) T-100-WM (n = 8), or (2) T-150-WM (n = 8); the remaining does formed two groups without male exposure (WOM), as follows: (3) T-100-WOM (n = 8) and (4) T-150-WOM (n = 8). To evaluate ovarian activity, blood samples were collected from all does on Days 2–4 during the 14-day period after the male exposure. On Day 12, all does exposed to males (16/16), irrespective of the nutritional treatment, depicted ovulatory activity, whereas only 3/16 (18.75%) T-WOM does did, indicating a significant (P < 0.001) difference between these treatment groups. The increased nutritional level of the T-150 group during the anoestrous season did not result in an early onset of ovulatory activity. Does demonstrated similar metabolic hormones and concentrations of blood metabolites between the two nutritional treatments (100 v. 150% of the nutritional requirements), suggesting a high physiological plasticity between the groups, stabilising their metabolism according to the nutritional history female goats faced, and generating similar reproductive outcomes. The male effect seems to be enough to induce oestrus during the late anoestrous season, irrespective of BCS and BW.