ABSTRACT. Buck effect, Caprine, Capra hircus, Nulliparae. KEYWORDS

EFEITO DO MACHO E REDUÇÃO DAS ESTAÇÕES DE MONTA EM DIFERENTES CONDIÇÕES CLIMÁTICA A REPRODU- ÇÃO DE NULÍPARAS ANGLO-NUBIANA Male Effect and Breeding Season Shortening Un- der Contrasting Climatic Conditions Upon Repro- duction of Nulliparous Anglo-Nubians

ABSTRACT

This study was aimed to evaluate breeding seasons of different durations under contrasting climatic conditions upon reproductive performance of nulli- parous does submitted to male effect. A total of 240 Anglo-Nubian females at 8 to 12 months of age were used and were kept away from all three bucks at a distance of 300 m for 60 days, which avoided any physical, visual, olfactory or hearing contact between genders. Estrus were visually detected and pregnancy rates were determined by ultrasonography 60 days after the last mating. Bree- ding season duration and climatic condition did not influence estrus incidence, where 70% does had estrus detected at the dry season, 80% of does cycled at the rainy season within breeding seasons of 25 days. Moreover, 80% of does cycled at the dry season and 95% at the rainy season during breeding seasons of 35 days and 45 days. After breeding seasons of 25 days, pregnancy rate was lower at the dry season (55.0%) compared to the rainy season (80.0%). Mean birth weight of resulting offspring was lower during the rainy season (2.94 kg ± 0.26) than during the dry season (3.03 kg ± 0.16). The results show that estrus onset is affected by breeding season durations and climatic conditions tested, although dry season lowered pregnancy rates. In conclusion, 25-day breeding seasons are recommended to improve standardiza-tion of offspring lots, to reduce costs with food supplementation and estrus detection, while pre-serving pregnancy and ki- dding rates.

K E Y W O R D S Buck effect, Caprine, Capra hircus, Nulliparae.

INTRODUCTION

The technological progress in goat produc- tion during the last decades through commercia- li-zation of semen, embryos and live animals of superior genetics has accelerated genetic improve- ment programs. However, this progress has been heterogeneous across countries and production systems, and several producers still need technical

support in order to adopt more rational manage- ment prac-tices aiming to increase productivity and profitability throughout the year (GUIMA- RÃES FILHO and CHARLES, 1983; SILVA and ARAÚJO, 2000), especially under less favorable regions such as semiarid conditions (BANDEIRA et al., 2004).

It is advisable to adjust the breeding sea- son to nulliparous goats under semiarid conditions

1Departamento de Medici- na Veterinária, Universidade Federal Rural da Amazônia,

2Departamento de Medicina Veterinária, Universidade Fe- deral Rural de Pernambuco,

3Departamento de Medicina Veterinária, Universidade Fe- deral de Sergipe. *maiana-@

hotmail.com

Luiz Rennan Sampaio OLIVEIRA 1, José Carlos FERREIRA-SILVA 2, Maiana Silva CHA- VES 2,*, Leopoldo Mayer de FREITAS NETO 2, Marcelo Tigre MOURA 2, Eduardo Luiz Cavalcanti CALDAS 3, Paulo Fernandes de LIMA 2, Marcos Antonio Lemos OLIVEIRA 2

using the male effect in order to allow the control and stimulation of reproductive activity under natu- ral conditions (HORTA and GONÇALVES, 2006;

LIMA et al., 2000). This procedure allows kidding under shorter time intervals, reducing time and ef- fort investment for delivery assistance and further racionalizes other management practices (VALLE et al., 2000). Moreover, this approach also contri- butes to select females with higher prolificacy and with better maternal behavior (MEDEI-ROS et al., 1994; SILVA and ARAÚJO, 2000).

The male effect stimulus over reproducti- ve activity of nulliparous females depends upon ma-turity of reproductive organs, ovarian activity, adequate reproductive hormone profiles (QUIRKE et al., 1981) and their capacity to attract and sti- mulate male reproductive behavior (GELEZ and FA-BRE-NYS, 2004). Moreover, factors such as breed, live weight, age, sexual experience and so- cial-sexual interactions may influence reproducti- ve events (GONZALEZ-STAGNARO et al., 1993;

GELEZ et al., 2003).

The work was aimed to evaluate the repro- ductive performance of nulliparous females sub- -mitted to male effect in breeding seasons of 25, 35 and 45 days during dry and rainy periods under semiarid conditions.

Material and Methods

The experiment was previously approved by the ethics committee at the institution Pio Dé- -cimo, document number 08/12. The experiment was conducted in Sertânia - PE, with geographic coordenates, 9.107.002 KmN and 691.005 KmE, altitude of 558 m, semiarid weather, mean annual temperature of 25º C, mean annual rainfall of 431 mm3, with rainy period from February to June.

A total of three bucks with age ranging from 24 to 48 months, and 240 nulliparous Anglo-Nu- bian females with age ranging from 8 to 12 months were used in the experiment. Females were identi- fied with plastic ear tags, weighted and evaluated for body condition score as previously de-scribed (GONZALEZ-STAGNARO, 1991).

Females were raised under semi-extensive conditions, being fed with native pastures (Cy- no-dia vulgaris, L., Mimosa nigra, Hub., Cordia leucocephala, Moric., Bauhinia cheilanta, Steud.,

Pithecolobium diversiffolium, Benth.), cultivated pasture (Cenchrus ciliaris, L.) and had free access to mineral salt and water. Exclusively during the dry period, all animals were further supplemented with hay silage (Pennisetum purpureum, Schum.).

Bucks with proven fertility were kept in individual pens and fed with fresh hay (Pennise- tum purpureum, Schum.) and supplemented with 200g concentrated goat feed (Durancho®) and 200 g grain corn (Zea mays, L) per animal / day. Bucks remained apart from females at a distance of 300 m for 60 days (male effect preconditioning period) without any physical, visual, olfactive and audi-ti- ve contact between genders. After introduction in the female lot, bucks were submitted to the same feeding conditions than females.

Bucks were submitted an andrology exam the day before breeding season onset in order to confirm their reproductive status (CBRA, 1998).

Bucks were marked with a mixture of grease and ink (4:1) in the sternum bone region to allow visual detection of females that cycled (bucks were re- -marked with ink of different color every 10 days).

The mating events and females marked with ink were observed daily by trained personnel at 6:00 and 16:00 hours for one hour periods.

Mating events during the Dry period were detected from October 27th until December 10th, and during the rainy period from May 18th until July 3rd, under breeding seasons of 25, 35 and 45 days. During the dry period, females (n = 120) had a mean live weight of 26.76 ± 2.36 Kg, with mean body condition score of 3.05 ± 0.21 and during the rainy period females (n = 120) had a mean live weight of 25.65 ± 0.67 Kg, with mean body condi- tion score of 3.05 ± 0.21.

The reproductive status of females was evaluated by ultrasonography (SANTOS et al., 1985), vaginoscopic exam adapted from bovine report (GRUNERT et al., 2005). Pregnancy diag- no-sis was performed by ultrasonography on day 60 after the last mating recorded, as previously de-scribed (SANTOS et al., 1985). The results were analyzed by ANOVA for continuous data and Tukey’s test for mean comparisons and Chi-square test for comparisons between proportions. The sig- nificance level was 5%.

Results

Pregnancy type influenced birth weight du-

ring the rainy period (P < 0.05), were kids from

twin deliveries had lower birth weight than single-

ton kids (Table 3).

Breeding season duration did not affect the percentage of females displaying estrus, irre-spec- tively of climatic conditions (Table 1).

Pregnancy rates were similar between bree- ding seasons of different duration (P > 0.05), howe- ver, the dry period negatively affected pregnancy rates (Table 2).

Discussion

The high number of animals that cycled, irrespectively of breeding season duration and cli- -matic conditions is probably due to the male effect stimulus to female reproductive activity. As de-s- cribed by several authors (SHELTON, 1960; OTT et al., 1980; LIMA et al., 2000), a sudden intro-duc- tion of a male after isolation for 3 to 4 weeks wi- thout any visual, olfactive and auditive, pro-vokes a LH pre-ovulatory peak that stimulates follicular development that leads to ovulation (MARTIN et al., 1986; CHEMINEAU, 1987). Despite the fact that estrous percentage did not dif-fer between groups and that estrus incidence was similar to previous reports for nulliparous and pluriparous females (LIMA et al., 2000; LUNA-OROZCO et al., 2008), it is relevant to note that under breeding season of 25 and 35 days, some does mated twi- ce. This finding suggests that a breeding season of 25 days allows the reduction in costs with trained personnel for estrous detec-tion and other mana- gement expenses, while allowing all females a se- cond opportunity to be bred and become pregnant.

Pregnancy rates were not affected by bre- eding season duration, a fact that further suggests that shortening of breeding season duration is possi- ble, despite suggestion the literature and com-mon practices among farmers of 45-60 day breeding se- asons (MEDEIROS et al., 1994). In contrast, does bred during the dry period had lower pregnancy rates, irrespectively of breeding season dura-tion.

Pregnancy rates were accordingly to previous data on pluriparous Anglo-Nubian does (LIMA et al., 2000; MEDEIROS et al., 2004), however, pregnancy rates were affected by varying climatic conditions. during the dry period, native and cul- tured pastures are severely affected and nutritional composition lowers drastically (LOTTHAMMER, 1979; ANDRIGUETTO et al., 2004). It cannot be ruled out that, even under further supplementation

with hay silage, nutritional requirements for cy- cling females may have not been met during the dry period. This fact that may have particularly affected LH concentration and ovarian function and progesterone production by the corpus luteum (ANDRIGUETTO et al., 2004; RAKES et al., 1985).

Female goats are proliferous and hold high percentage of multiple pregnancies, despite varia- -tions in climatic conditions (LIMA et al., 2000).

As described here, the number of females with twin pregnancies was lower than previously repor- ted with pluriparous females (LIMA et al., 2000;

MEDEIROS et al., 2004). This discrepancy may be due to the reduced size of uterus in nulliparous, that may lead to conceptus death or gamete of low competence (MEDEIROS et al., 2004). Finally, it can also be suggested that energy nutritional demands were not efficiently met. The percenta- ge of twin pregnancy was similar within climatic periods, possibly due to unexpected high rainfall during the breeding season. Goats raised under se- miarid conditions are less adapted to high humidity con-ditions, which result in less feeding behavior that may lead to weight loss.

Singleton offspring have higher birth wei- ght than twin offspring (MAIA and COSTA, 1997;

RIBEIRO et al., 1998; SILVA and ARAÚJO, 2000;

MEDEIROS et al., 2004). As described here, this difference on birth weight was not observed, but climatic conditions did affect kidding weight. This result is due to does being mated during the rainy period and delivering in the dry period and those females mated during the dry period delivered du- ring the rainy period. Fetus growth is accen-tuated in the final third period of pregnancy (BONFIM and BARROS, 2006), which were concom-itant with abundant rainfall for all breeding seasons, supporting forage production and presumably ade- quate nutritional support for pregnant females. Me- deiros et al. (2004) described intense variation of forage quantity and quality under semiarid condi- tions, and its strong influence of kidding weight.

Conclusion

The estrus manifestation in nulliparous

goats is not correlated with breeding season dura-

tion and climatic conditions under the male effect, however, pregnancy rate is reduced in the dry pe- riod. Moreover, breeding seasons of 25 days should be recommended since it allows the production of more homogeneous offspring lots, reduced feeding supplementation requirements and demand for trained personnel aiming to detect estrus.

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