Influence of nutritional and socio-sexual cues upon reproductive efficiency of goats exposed to the male effect under extensive conditions

Abstract

This study evaluated the effect of nutritional supplementation and socio-sexual cues upon reproductive efficiency of goats exposed to the male effect under rangeland grazing conditions (22 degrees N). Criollo goats (n = 73) were distributed in four experimental groups: (1) continuous males (CM, n = 19) in which males (n = 2) remained together with females from 7 March to 28 July; (2) supplemented males (SM, n = 16) in which males (n = 2) were kept separately and were individually supplemented with 18% crude protein and 2.77 Mcal ME kg(-1) DM, during a 30-day period; (3) supplemented males exposed to the female effect (SM + FE, n = 19), in which supplemented males (n = 2) were maintained with females induced to oestrus before being used for male effect; and (4) supplemented males and supplemented females (SM + SF, n = 19) in which males (n = 2) were supplemented as in group SM, and females received the same supplementation as males 30 days before and 30 days after male introduction. Grazing was performed from 0900 to 1900 hours; liveweight (LW) was registered weekly before grazing and (or) supplementation. Ovarian activity was evaluated (serum P4 concentrations) in the four groups before and after male introduction. At the beginning of the study and supplementation, female LW did not differ among treatments (P > 0.01). However, during the supplementation phase, LW increased in a different fashion among groups (P < 0.002), favouring the SM, SM + FE and SM + SF groups. A positive correlation between female LW at the beginning of the rainy season and the onset of ovulatory activity was observed (r = + 0.90; P < 0.01). The average date for the onset of ovarian activity differed (P < 0.001) among groups, being earlier in the SM + SF group (9 May +/- 4.3 days), which also depicted the shortest interval between the introduction of males until the onset of ovulatory activity (P < 0.001). Results of the present study indicate that nutritional signalling of the reproductive activity of both female and male Criollo goats reared under marginal conditions surmounts the inhibitory effects of long-day photoperiods during the non-reproductive season. An increased level of nutrition during the anestrous season may be used to increase reproductive function of both male and female goats reared in harsh nutritional conditions and applied as a green, clean, and ethical reproductive tool at these latitudes.