Effect of buck stimulus on mature and pre-pubertal
norgestomet-treated goats
M. Mellado
*, R. Olivas, F. Ruiz
Depto. ProduccioÂn Animal, UAAAN, Saltillo, Coah, Mexico
Accepted 14 September 1999
Abstract
Two experiments were conducted to assess the effect of buck exposure to synchronize estrus in mature and pre-pubertal norgestomet-treated crossbred (criollodairy breeds) goats. In experiment 1, 100 mature goats (25 per group) under range conditions were either teased at 48 or 24 h before Sincromate-B (SMB; 9 days treatment of 2 mg norgestomet) implant withdrawal. A third group was exposed to bucks 1 day after SMB treatment and another group was only exposed to bucks (control). Does exposed to bucks 1 day after SMB treatment tended to have a lower percentage of estrus (70% compared to 80% and 92% in other groups) and lower pregnancy rate (57.9 compared to 78.3 and 82.6 in other groups). At 156 days post-joining a signi®cant (P< 0.05) difference in cumulative kidding percentage was found between does teased 48 h before implant removal (88.9%) and does teased 24 h before implant removal (56.3%). Teasing without norgestomet was completely effective at stimulating estrus activity. In experiment 2, pre-pubertal does (n36; mean 16.6 kg BW) treated with SMBPMSGteasing tended to have a higher estrus response than SMBPMSG treated female goat kids (91.6% vs. 66.6%;P0.13). The results of this study indicate that, during the transitional period, the male effect was as effective as the synchronizing treatments involving SMB in inducing estrus in goats with reduced seasonal inhibition of reproduction. Also, buck exposure potentiates the effect of PMSG to induce estrus in norgestomet primed pre-pubertal does.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Estrus synchronization; Goat; Norgestomet; PMSG; Buck effect
1. Introduction
A variety of estrus synchronization regimes for sheep and goats indicates that, during the nonbreeding or transitional period, the administration of PMSG,
hCG, hMG, FSH or GnRH enhances the ovulatory response of progestagens-treated animals. However, the use of these gonadotropins increases markedly the cost of the synchronization scheme and occasionally reduces fertility in those does repeatedly treated with PMSG, as a result of the immune response against this hormone (Baril et al., 1992). Moreover, multiple injections of GnRH (Knight et al., 1988) or FSH (Pendleton et al., 1992) are required to obtain a preovulatory LH peak in progestagen-treated animals. *Corresponding author. Tel.:52-84-17-30-22;
fax:52-84-17-37-84.
E-mail address: mmelbos@uaan.mx (M. Mellado)
An inexpensive alternative to induce ovulation dur-ing the nonbreeddur-ing season in moderately seasonal goats, could be the use of the buck effect in combina-tion with a progestagen. This exteroceptive stimulus increases plasma LH concentration in does within a few minutes (Chemineau et al., 1984, 1986a,b) and the preovulatory LH surge and ovulation occur 1±3 days after initiation of teasing (Chemineau, 1987). Studies in sheep have shown that teasing during or after a progestagen treatment increases the number of ewes exhibiting estrus (Lewis and Inskeep, 1973; Quinlivan, 1970; Umberger et al., 1994), increases conception rate at ®rst service period (Lewis and Inskeep, 1973; Rajamahendran et al., 1993) and reduces lambing intervals (Lewis and Inskeep, 1973; Wheaton et al., 1992). Similar studies appar-ently has not been done in goats, therefore it was proposed to test whether the introduction of bucks during the transitional period enhances the estrous response and reproductive performance of norgesto-met-treated goats.
2. Material and methods
2.1. Site and management
2.1.1. Experiment 1
One hundred multiparous goats of undetermined genotype (mixture of criollo and dairy breeds) weigh-ing 39.43.7 kg and in late lactation were used in this study. Does were maintained on arid range in north-east Mexico (258070
N, 1018400
W; mean annual rainfall299 mm), without supplementation throughout the year. The does were randomly allo-cated to four treatment groups (n25 per group), during the transition period (last week of May). The four groups then received the following treatments: (1) Syncro-Mate-B (SMB, norgestomet) with expo-sure to fertile bucks 1 day after SMB treatment; (2) SMB plus teasing starting 48 h prior to implant removal; (3) SMB plus teasing starting 24 h prior to implant removal; and (4) teasing only (control). Teasing was carried out with 4 fertile bucks (2 Nubian and 2 Boer goats).
The SMB treatment consisted of a subcutaneous implantation at the back of the ear of 1/3 of the SMB implant used for cattle (approximately 2 mg
norgestomet), accompanied by an intramuscular injection of 0.75 mg norgestomet and 1.25 mg estra-diol valerate. On day 9 following implantation, the implant was removed through a small incision made in the skin at the distal end of the implant. At the end of the 9 days treatment period all goats in each treatment group were exposed to 4 fertile bucks on June 3 for a 30 days breeding period. Does were checked daily, 1 h in the morning and 1 h in the afternoon, for signs of estrus. During the parturition period individual doe kidding information was col-lected on a daily basis.
2.1.2. Experiment 2
Thirty-six pre-pubertal crossbred female goat kids (Criollodairy breeds; 6-month-old and 16.5 kg mean BW) were utilized in this study. Feeding, man-agement conditions and SMB treatment were similar to those described in experiment 1. During the breed-ing period (February, dry season) goat kids were allocated at random (12 per group) to the following treatments: (1) SMB300 UI PMSG; (2) SMB 300 UI PMSGteasing; and (3) teasing only. PMSG was administered on 7 days after implantation and all goats received 50 mg progesterone one week previous to the norgestomet treatment. One native intact buck ®tted with an apron, which impeded copulation, was used as teaser. Teasing began 24 h prior to implant removal. Does were observed twice daily for signs of estrus for a period of 4 days. Because of the reduced availability of forage on range it was not possible to serve the female goat kids in estrus.
2.2. Statistical analysis
Percentage of does showing estrus and proportion of does pregnant was compared using chi-square procedures. The interval to estrus and proli®cacy were analyzed using a one way ANOVA.
3. Results
3.1. Experiment 1
exposed to bucks after the SMB treatment tended to be lower, compared to does in other treatments. A longer (P< 0.01) interval to estrus was observed in does exposed to bucks but not treated with SMB. Concep-tion rate at the ®rst post-treatment estrus of goats teased after the SMB treatment was lower (P0.08) than that of goats teased before the end of the SMB treatment. There were no signi®cant differences in proli®cacy due to treatment.
The cumulative kidding percentages for does in the different groups are presented in Fig. 1. A signi®cant (P< 0.01) difference in cumulative kidding percen-tage was evident at 154, 156 and 158 days from ®rst exposure to bucks between SMB-treated does (with or without teasing during the norgestomet treatment) and nontreated goats. Also, on day 156 post-introduction of bucks a greater (P< 0.05) per-centage of goats teased 48 h prior to implant removal kidded as compared to does teased 24 h prior to implant withdrawal.
3.2. Experiment 2
Estrus response and mean intervals from cessation of treatment to estrus for pubertal does are pre-sented in Table 2. The percentage of does showing
estrus tended to be greater in the teased, SMB-PMSG-treated does than in control (only teased) does. Estrus response of SMB-PMSG-treated does was intermedi-ate between control and SMB-PMSG-teased does. Table 1
The effect of a 9-day norgestomet treatment in combination with teasing on the estrous response and reproductive performance of crossbred goats under range conditions (percentages in brackets)a
Item Treatments groups
Control (teasing only)
SMBbuck 1 day after treatment
SMBbuck 2 days before end of treatment
SMBbuck 1 day before end of treatment
Number of goats 25 25 25 25
Number of goats showing estrusb 23a(92) 19b(76) 23a(92) 20a(80) Interval to estrus (h;xSE) 11510.4 70.06.8 54.25.3 64.86.1
First post-treatment estrus
Does conceiving 19A(82.6) 11B(57.9) 18A(78.3) 16A(80)
Kids born/does treated 1.36 0.68 1.12 1.0
Kids born/goat kidding (xSE) 1.79a0.10 1.55a0.16 1.56a0.12 1.56a0.13 All estrus during 30 days
Goats returning to service 4 8 5 4
Abortions 1 3 2 2
Does kidding/does treated 23 (92) 21 (84) 22 (88) 21 (84)
Does conceiving 24 (96) 24 (96) 24 (96) 23 (92)
aFigures in the same row with different a, b labels are different (P< 0.12); whereas different A, B labels are signi®cantly different (P< 0.08).
bEstrus response in 5 days synchronized period in treated does and 8 days period in control does.
4. Discussion
It was evident that stimulation with buck at the end of the SMB treatment played a signi®cant role in the synchronization of estrus and pregnancy rate in nor-gestomet-treated does during the transitional period. This is in accordance with results by Umberger et al. (1994) who found that the ram effect was as effective as PMSG-hCH in stimulating luteal activity in pro-gestagen-primed ewes.
Both estrus response and pregnancy rate at estrus subsequent to the induced estrus tended to be lower in does not teased during the SMB treatment, compared to does in other treatments. These results are in agree-ment with reports in sheep (Umberger et al., 1994) and goats (Greyling and Van Nierkerk, 1991) where pro-gestogen treatment alone has been inadequate for the induction of synchronized estrus in seasonally anov-ular animals. Moreover, in the absence of PMSG or buck stimulus, not all goats showing behavioral estrus after a progestagen treatment present ovulation, but treatment with 500 UI PMSG at progestagen removal insures ovulation (Dhindsa et al., 1971).
Introduction of bucks 48 h before withdrawal of the SMB implant as compared to 24 h before withdrawal increased the cumulative percent of does kidding during the ®rst week of the kidding season. By 156 days post-joining, 89% of does joined to bucks 48 h before implant removal had kidded, whereas only 56% of does in contact with bucks 24 h before implant withdrawal had kidded. This pattern was not re¯ected in the average time to onset of the induced estrus because presence of the buck 48 h prior to implant removal only shortened 10 h the interval to estrus (nonsigni®cant), compared to exposure to bucks 24 h before explantation. Buck stimulus increases
plasma LH concentration in does within a few minutes of contact (Chemineau et al., 1984, 1986a,b), and the preovulatory LH surge and ovulation occur 1±3 days after initiation of teasing (Chemineau, 1987). Thus, teasing 48 h previous to implant removal apparently hastened ovulation after the SMB treatment giving a more concentrated kiddings. It is worth mentioning that buck stimulus seems to be independent of steroid feedback on the hypothalamic centers controlling the secretion of LH (Martin et al., 1983).
In other studies the ram effect combined with progestagens has been bene®cial either when rams are joined upon progestagen removal (Lewis and Ins-keep, 1973; Wheaton et al., 1992; Umberger et al., 1994) or at the beginning of the progestagen treatment (Rajamahendran et al., 1993). In the same zone in which this study took place, it has been shown that the introduction of bucks at the time of SMB implantation results in a high proportion of does in estrus with the implant in situ (Mellado and ValdeÂz, 1997). Therefore in moderately seasonal goats it does not seem perti-nent to start the teasing process before 48 h before implant removal.
Teasing without norgestomet (control group) was completely effective at stimulating estrus activity during the transitional period. By 8 days after joining, most does had shown estrus and percentage of does conceiving was comparable to that of SMB teased-goats. Goats in the control group would be expected to respond to teasing within 5 days, and then experience a short cycle and mate again from around the eighth day (Chemineau, 1983). The cumulative kidding data supports this interpretation, as the control does showed a similar synchronization of kidding to other groups, with kidding concentrated into a 10 day period. This concentration of kidding was delayed Table 2
Estrus response and interval after treatment to estrus of prepubertal goats treated with SMB, PMSG and the stimulus of the bucka
Treatment group BW (kg) In estrus Interval to estrus
(h;xSE)
Number %
SMBPMSG 16.96 8/12 66.6a 35.7A2.7
SMBPMSGBuck 16.78 11/12 91.6b 31.6A2.4
Buck exposure 16.40 2/12 16.6c 60.0B0.0
by approximately 6 days, the normal short cycle interval length, compared to other treatments. In the treatment groups it was expected that the short cycles are to be eliminated by the progestational treatment (Chemineau, 1985). Again, the cumulative kidding supports this interpretation as the kidding occurred 6 days earlier than the control group.
Although nonsigni®cant, the control group showed a signi®cant elevation in fecundity (1.79 kids per doe kidding) which means that 24% more kids were born than in the treated groups (41 vs. 33 kids). This would seem to be a considerable economic advantage to farmers. Thus, if reduced kidding intervals are not economically important for producers, teasing is the only adequate means to synchronize estrus of does at the end of spring.
In experiment 2, teasing alone resulted in a poor estrus response in the pre-pubertal female goat kids, but teasing combined with PMSG had a synergistic effect on estrus response of norgestomet-primed goat kids. The elevation and maintenance of pulse fre-quency and basal concentrations of LH brought about by the buck stimulus plus the administration of PMSG probably created a chronic gonadotropin stimulus that ultimately induced estrus in these pre-pubertal ani-mals. Advancement of the onset of the pubertal estrus in ewe lambs (Al-Mauly et al., 1991; Kassem et al., 1989; Oldham and Gray, 1984) and female goat kids (Amoah and Bryant, 1984) by the presence of the male, has also been documented.
5. Conclusions
From the current results it would appear that, during the transitional period, farmers in the zone where this study took place should not use synchronizing treat-ments involving progestagens, but rely on natural teasing. Also, in pre-pubertal goats the presence of the buck seems to potentiate the effect of PMSG and therefore constitute an important stimulus to induce the pubertal estrus in does.
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