M.C. Gatica

Role of body condition score and body weight in the control of seasonal reproduction in Blanca Andaluza goats

The reproductive activity of 84 female Blanca Andaluza goats was monitored over 17 months to determine the role of body condition score (BCS) and body weight (BW) in its control. Following a 3×2 factorial experimental design, the animals were allocated to three groups: low BCS (≤2.50, n=24), medium BCS (BCS=2.75-3.00, n=31) and high BCS (≥3.25, n=29). The same animals, irrespective of the BCS group categorization, were also divided into two groups depending on BW: low BW (≤40kg, n=44) and high BW (>40kg, n=40). Oestrus was evaluated daily using vasectomised males. The ovulation rate was assessed by trans-rectal ultrasonography after the identification of oestrus. Ovulations were determined by monitoring the plasma progesterone concentration weekly. The BCS and BW were recorded once a week and nutritional status adjusted to maintain the initial differences in BW and BCS between the groups. Both BCS and BW had a significant (at least P<0.05) influence on the onset, the end, and the duration of the breeding season, with longer periods of reproductive activity recorded in does with a BCS of ≥2.75 and BW of >40kg. No significant interaction between these variables was observed. Some (11.7%) of the does in the groups with animals of BCS≥2.75 had ovulations during seasonal anoestrus. None of the does with a BCS of ≤2.5 had ovulations during seasonal anoestrus. The ovulation rate of the first and last oestrus was influenced by BW (P<0.01). These results demonstrate that Blanca Andaluza goats show marked reproductive seasonality that is clearly and independently modulated by BCS and BW.

Influence of the male effect on the reproductive performance of female Payoya goats implanted with melatonin at the winter solstice

This research addressed the effect on reproductive performance of melatonin implants inserted at the winter solstice in Payoya goats. Female goats (n = 100) were divided into two experimental groups, one subjected and the other not subjected to the male effect. Half of each group was implanted with melatonin at the winter solstice; the remaining animals received no such hormone treatment. Oestrous activity, as detected by visual observation, was recorded daily using melatonin implanted bucks. Trans-rectal ultrasonography was used to estimate of time of ovulation. Corpus luteum activity was confirmed by plasma concentrations of progesterone greater than 0.5 ng/mL. Fecundity, fertility, prolificacy and productivity were calculated. Neither the male effect nor melatonin treatment alone influenced reproductive performance. The greater fecundity and fertility: 91.7% (P < 0.05) was obtained with melatonin implantation plus the male effect. Greater productivity occurred when melatonin was used (1.02 ± 0.10 compared with 0.76 ± 0.66 mean number of kids per female for melatonin and non-melatonin treated groups, respectively, P < 0.05). The present results show that the fertility of female Payoya goats implanted with melatonin at the winter solstice can be improved by subjecting females to the male effect. Moreover, productivity of does is enhanced when melatonin implants are used in comparison to productivity of non-treated females.

Exogenous melatonin does not improve the freezability of Blanca Andaluza goat semen over exposure to two months of short days.

This paper compares the effects of exposure to exogenous melatonin (MEL), short days (SD, 8h of light) and long days (LD, 16 h of light), on reproductive activity, sperm motility and other reproductive variables, in Blanca Andaluza bucks. Fourteen males were spilt into two groups of seven animals (G1 and G2). They were subjected to five alternations of 2 months of LD followed by 2 months of SD or MEL before the experimental period of three consecutive intervals of: (1) 2 months of SD (G1, N=7) or MEL (G2, N=7); (2) 2 months of LD (G1+G2, N=14); and (3) 2 months of SD (G2, N=7) or MEL (G1, N=7). Plasma testosterone concentration, live weight, testicular weight and fresh semen quality were determined weekly. Semen was also cooled and frozen-thawed every fortnight, and the same quality variables measured as for fresh sperm. When the bucks were under LD treatment, the testosterone concentration was lower than when under MEL or SD treatment (P<0.01); values for the semen concentration and total number of sperm per ejaculate were also higher (P<0.001). No differences were observed between the MEL and SD treatments in terms of fresh, cooled or frozen-thawed sperm quality. Only some quality variables on fresh semen were improved by MEL and SD treatment (P<0.05). In conclusion the results of the present experiment showed that MEL improved the fresh semen motility variables, but this did not improve the motility of frozen-thawed sperm over that recorded for either SD or LD treatment.

Exogenous melatonin after a treatment of artificial long days is able to increase LH secretion during seasonal anoestrus in Payoya goats

One experiment was conducted to determine whether the treatment with artificial long days and exogenous melatonin can increase, by itself, luteinizing hormone (LH) secretion during spring (seasonal anoestrus) in Payoya goats and whether this treatment causes a variation in the reactivation of the LH secretion in the normal breeding season. The experiment started on 4 November and finished on 27 October. A total of 22 ovariectomised-oestradiol treated goats were used. Ten goats were exposed to long days (16 h of light/day) from 14 November to 20 February. On 20 February, they received one s.c. melatonin implant and were exposed to natural photoperiodic changes in an open shed. The control group was located in another open shed with any treatment during the whole experiment. For both groups, plasma samples were obtained twice a week for LH assay. The photoperiodic treatment induced an earlier fall of the LH secretion. However, after the melatonin treatment, a clear increase of LH secretion during the natural seasonal anoestrus in the treated group was observed, and no difference in the onset of the LH secretion at the normal breeding season was observed. We can conclude that, in Payoya goats, the photoperiodic–melatonin treatment is by itself able to induce a clear LH increase during the seasonal anoestrus and does not modify the reactivation of the LH secretion at the normal breeding season.

When using photostimulated bucks to induce the male effect in female goats living at Mediterranean latitudes, a male: female ratio of 1:20 is optimum

ABSTRACT This study examines the reproductive response and reproductive performance of does subjected to the male effect at different male:female ratios when photostimulated males are used. One hundred and thirty does were distributed homogeneously into six groups with male:female ratios of either 1:30 (two repetitions of 30 females with one male each), 1:20 (20 females with one male), 1:15 (15 females with one male), 1:10 (20 females with two males), or 1:5 (15 females with three males). After the introduction of the males (all made sexually active by keeping them for three months under long days), oestrous activity was recorded daily by direct visual observation of the marks left by marking harnesses worn by the males. Ovulation was confirmed via the plasma progesterone concentration. Fecundity, fertility, prolificacy and productivity values were also determined. The 1:30 group returned the lowest percentage of does that ovulated and that showed oestrous activity; it also returned the lowest fecundity and fertility values. The highest values for all these variables were recorded for the 1:5–1:20 groups (with no significant difference between them). These results show that, under Mediterranean latitudes, the reproductive response, fecundity and fertility are diminished when the photostimulated male:female ratio is very low (1:30). The optimum ratio would appear to be around 1:20.

Reproductive responses to sexually active buck of does treated with melatonin when body weight/body condition is increasing or decreasing

When the sexual activity of bucks is minimal, there is a minimal male effect on does regardless of their body weight (BW)/body condition (BC) and whether does are treated with melatonin or not. The study examines whether sexually active bucks can induce an adequate male effect in does with an increasing or decreasing trajectory of change in BW/BC when does are or not treated with melatonin. During natural anoestrus, 46 Blanca Andaluza does were assigned to two groups: 1) low BW/low BC group in which does were fed 1.9 times maintenance requirements for dietary energy for gaining BW/BC (LLg group; n = 23); or 2) a high BW/high BC group in which the does were fed 0.4 times maintenance requirements for dietary energy that resulted in a loss of BW/BC (HHl group; n = 23). There were similar numbers of does in each group that were treated or not treated with melatonin (MEL). Following 48 days of isolation from bucks, four sexually active individuals fitted with marking harnesses were transferred to the paddock containing the does of each group. Blood samples were collected by jugular venipuncture (before the distribution of concentrate) twice per week. The effect of the treatments (increasing or decreasing BW/BC and melatonin) on the different variables that were assessed were analysed using an ANOVA or the Fisher-Freeman-Halton exact probability test as necessary. During the 35 days after treatments were applied, the percentage of females expressing oestrous and having an ovulation were greater in the LLg + MEL than HHl-MEL subgroup (P < 0.05). The interaction of nutrition × melatonin treatment had a significant effect on reproduction of does (P < 0.05). This could be explained by the greater plasma glucose and IGF-1 and lesser plasma non-esterified fatty acid concentrations in does with increasing BW/BC (P < 0.01), and the greater IGF-1 concentrations of MEL-treated females (P < 0.01). The LH concentration and pulsatile release of this hormone from the pituitary were also modified by the presence of the males (P < 0.01). Furthermore, the LLg + MEL-treated does were responsive to the presence of bucks (P < 0.05). The present results indicate sexually active males cannot induce an adequate reproductive response in females with decreasing BW/BC even when does are being treated with melatonin. The presence of bucks enhanced the doe reproductive response when does were treated with melatonin and a pattern of increasing BW/BC.

Body condition score is a critical factor determining the onset of puberty in Blanca Andaluza female goat kids

This study examines the effect of body condition score (BCS), independently of bodyweight (BW), on the onset of puberty in Blanca Andaluza female kids born in Autumn (November). Thirty-six female kids were distributed into three groups according to their BW and BCS: low BW and low BCS (LL, n = 10), low BW and high BCS (LH, n = 10), and high BW and high BCS (HH, n = 16). Feeding was adjusted weekly so that the animals would gain ~50 g per day. Oestrus was checked daily using young vasectomised bucks fitted with a marking harness. The ovulation rate was determined by transrectal ultrasonography 10 days after the identification of oestrus. Plasma samples were obtained weekly for progesterone determination. Changes in BW and BCS were also recorded weekly. The BCS had a clear effect on the date of first ovarian activity and first detected oestrus. The HH kids experienced the earliest onset of puberty (31 August ± 2.4 days) although no significant difference was seen compared with the LH group (19 September ± 8.7 days). A significant difference was recorded, however, in comparison with the LL group (25 October ± 7.8 days) (P < 0.001). No effect of BCS was observed on ovulation rate. These results show that, in Blanca Andaluza female kids, the onset of puberty depends strongly upon BCS. There may be clear benefit in breeding November-born animals if, during the prepubertal period, they can be maintained with a high BCS.