Reproductive status following artificial insemination in Sanga cows in the Accra Plains of Ghana

F Y Obese, K A Darfour-Oduro, E Bekoe, B A Hagan and Y Gomda

CSIR-Animal Research Institute, P.O. Box AH 20, Achimota, Ghana
fyobese@yahoo.com

Abstract

The reproductive performance records of 126 Sanga cows bred through artificial insemination (AI) at the Amrahia Dairy Farm from January 1998 to December 2007 were assessed.

The intervals from calving to first AI service, calving to conception and calving interval were prolonged. They averaged 158.8 ±8.9 days, 177.5 ± 9.5 days and 517.9 ± 13.5 days respectively. These parameters were not affected (P>0.05) by season of calving preceding AI, season of insemination or sex of calf.  The conception rate at first AI service and for all inseminations were low 42.6 % and 46.0% respectively. They were not affected (P<0.05) by the season of insemination. Gestation length averaged 281.6 ±1.4 days. The mean birth weight of calves was 25.7 ± 0.3 kg. Male calves had higher birth weights than female calves (26.9 ±0.4 versus 24.5 ± 0.5 kg; P<0.05).

Improving the nutritional status of the cows through strategic supplementation coupled with effective heat detection mechanisms and appropriate timing of AI, as well as efficient methods of storage, transport and handling of semen should improve the reproductive performance of cows.

Key words: conception rate, calving interval, nutrition, postpartum anoestrus

Introduction

Artificial insemination (AI) is a breeding technique used in the improvement of livestock. In 1994 the Ministry of Food and Agriculture in Ghana commenced a five-year National Livestock Services Project with an objective to increase meat and milk production to meet the protein needs of the population as well as reduce the country’s increasing dependence on livestock and livestock products through breed improvement using AI.

Although AI has been applied in cattle as a means of accelerated genetic improvement of the indigenous stock in Ghana, the overall productivity of animals has continued to be low. Some of the factors that contribute to this include inadequate management practices, poor nutrition, occurrence of reproductive disorders, systemic diseases and parasites.

Low conception rate is a major factor affecting the success of AI. Low conception rates can be caused by several factors and their interactions including those related to the cow, management of animal, AI services, semen quality and bull fertility (Nordin et al 2007). Apart from these, reproductive events such as occurrence of oestrus, ovulation, conception and embryonic mortality also influences conception rates. For example the short duration of estrus and the tendency to show estrus during the night, greatly affect the efficiency of artificial insemination (AI) programs in B. indicus cattle managed in tropical areas (Baruselli et al 2004).

The main objective of this study was to evaluate the reproductive performance of Sanga cows bred through AI at the Amrahia Dairy Farm in the Accra Plains of Ghana.  This would enable the development of measures to improve the efficiency of artificial insemination service provided at the Farm and also to smallholder farmers on the Accra Plains of Ghana. 

Materials and methods 

Location of study

The study was based on AI carried out between the period 1998-2007, on Sanga cows kept at the A.I Center of the Animal Production Departments’ Amrahia dairy farm located at Lat 05º 46' N and Long 00º 08'W  in the Accra Plains of Ghana. The mean monthly rainfall data in the area for the above period is presented in Figure 1. 

Total rainfall for the study period was 900.9 mm with an average daily temperature of 29^oC.  Rainfall was bimodal with peaks in June and October.  April to July was the major rainy season, and September to November represented the minor rainy season. The driest months were January, February, March, August and December (Figure 1). 

Management of animals

The Sanga cows were grazed from 08.00 to 15.00 h on natural pastures comprising Panicum maximum, Stylosanthes haemata and Sporobolus pyramidalis which constitute the dominant grass species in the grazing area. They were not given any supplementary feed. The animals had access to water from a dam twice daily in addition to water provided in the animal house ad libitum. Oestrus (heat) was observed twice daily at 06:00h and 18:00 h. A cow standing to be mounted (standing heat) was used as the main criteria for the cow to be assumed to be on heat therefore ready for insemination. Cows observed to be on heat in the morning were inseminated in the evening of that same day, while those which demonstrated signs of heat in the evening were inseminated the following morning. Friesian semen was used for insemination.

Data collection

Artificial insemination records on 126 Sanga cows from the Amrahia dairy farm were used. The records covered a 10-year period (January 1998 to December 2007). Parameters studied include interval from calving to first AI service, interval from calving to conception, calving interval, conception rate, gestation length and birth weight of calves. The effect of season of calving preceding AI service, season of AI service and sex of calf on the above stated parameters were evaluated. Conception rate was estimated using the following equation:

Statistical analyses

The general linear models (GLM) procedure of the Statistical Analysis Systems Institute (SAS 1999) was used in investigating days from calving to first AI, days from calving  to conception, gestation length, calving interval and birth weight of calf, and the effect season of calving preceding AI, season of insemination and sex of calf on these parameters. The following model was applied:

Y_ijk =µ + S_i + C_j+K_k +e_ijk

Where:

Y_ijk= days from calving to first artificial insemination, days from calving to conception, gestation length, calving interval and birth weight of calf.

µ  = overall mean 

S_i = effect of ith season of calving preceding AI

C_j= effect of the jth season of insemination; 

K_j = effect of kth sex of calf

e_ijk = a random error associated with each observation.

Differences between means were tested by LSMEANS. The effect of season of insemination on conception rate was assessed using the Chi-square test.

Results and discussion

Interval from calving to first AI service, interval from calving to conception and calving interval

The interval from calving to first AI, interval from calving to conception and calving interval, and the effect of season of calving or season of AI on these parameters are presented in Table 1.

The average interval from calving to first AI was prolonged and averaged 158.8 ± 8.9 days. This delay of first AI service after calving, particularly may be due to prolonged postpartum anoestrus (interval from calving to the resumption of ovarian cyclicity). This is most likely a result of inadequate nutrition (limited dietary energy and protein intake) and suckling management (Rutter and Randel 1984; Sasser et al 1988; Jolly et al 1995; Diskin et al 2003, Robinson et al 2006). Cows in this study were grazed on natural pastures. There was no supplementation of the cows with either crop residues, agro-industrial by-products or leguminous browse plants. During the dry season, the limited pasture available on the Accra Plains is of poor quality. In addition, there was lack of restriction on suckling by calves. 

Cows were allowed to suckle their young until they were weaned naturally between 6 to 9 months of age (Obese et al 1999; Okantah et al 1999; Okantah et al 2005). The low nutritional status of animals coupled with prolonged suckling stimulus could delay the resumption of ovarian cycles by interfering with the production and secretion of hormones important in ovarian follicular development and function in cattle. For example inadequate nutrition and suckling stimulus have been reported to reduce luteinising hormone pulsatility (Imakawa et al 1986; Williams et al 1996) and systemic concentrations of IGF-I (Nugent et al 1993; Roberts et al 1997) which are important in supporting the development, final maturation and ovulation of dominant follicles, leading to delayed ovulation and extended postpartum anoestrus period in cattle (Yavas and Walton 2000; Diskin et al 2003, Thatcher et al 2006).  The interval from calving to first AI service was not affected by season of calving preceding AI, season of AI or sex of calf.

The mean interval from calving to conception was 177.5 ±9.5 days and the calving interval was 517.9±13.8 days. These parameters were not affected (P>0.05) by season of calving preceding AI, season of insemination or sex of calf.  The calving to conception and calving intervals obtained in this study were higher than the 155.2±4.5 and 444.3±16.5 days respectively reported for the same breed on smallholder peri-urban dairy farms on the Accra Plains of Ghana (coastal savanna zone) (Obese et al 1999). It was also higher than the values of 149.7 ± 5.8 and 431±6.7 days reported for the same breed on smallholder farms in the humid forest zone in Ghana. The prolonged interval from calving to first AI obtained in the present study may have contributed to the extended calving to conception and calving intervals. Eduvie and Oyedipe (1991) have reported that the main determinant of long calving intervals is a prolonged postpartum anoestrous interval. Better management practices including improving the nutrition of cows by strategic feed supplementation especially during the dry season, as well as early weaning or restricted suckling of calves should shorten the postpartum anoestrous period and subsequently reduce calving to conception and calving intervals in these herds.

Gestation length

The gestation length obtained in this study was 281.6 ±1.4 days (Table 2).

It was similar to the value of 281.6 ±1.7 days and also compared favourably with the value of 291.8 ±16.1 days reported for the same breed in Ghana by Osei et al (1993) and Obese et al (1999) respectively.  Gestation length was not affected (P>0.05) by season of calving preceding AI, season of AI or sex of calf.

Birth weight of calves

The mean birth weight of calves was 25.7±0.3 kg and was affected by sex of calf (Table 2). Male calves had higher birth weights than female calves (26.9 ±0.40 versus 24.5±0.5 kg; P<0.05). Male calves are generally reported to be heavier than their female counterparts at birth (Fall et al 1982).  According to Pabst et al (1977), a longer gestation period of about a day or two for male calves than female calves brings about the difference in birth weight.

Conception rate

The conception rate (CR) at first service was 42.6 %, and 46.0% for all services (Table 3). 

The major reason for this low CR may to due to poor heat detection, inappropriate timing of AI, poor insemination technique or poor semen quality. The timing of insemination in relation to first detection of heat is critical for achieving high conception rates (Peters and Ball 1995; Tjiptosumirat et al 2007) as well as factors relating to the transport, storage, handling and thawing of semen in the field (Peters and Ball 1995). Although conception rate at first service or for all inseminations was not affected by the season of insemination, it however approached significance at (P=0.07), being higher in the major rainy season than in the minor rainy or dry season (Table 3). The abundant supply of good quality fodder during the major rainy season might have improved the body condition of cows thus improving their conception. Putting in place very effective heat detection mechanisms could result in reduction of undetected oestrus. Also, the appropriate timing of AI, coupled with good insemination technique and efficient methods of transport, storage, handling and thawing of semen should improve conception rate of cows.

Conclusion 

• The intervals from calving to first AI, calving to conception and calving intervals were prolonged. This may be due to prolonged postpartum anoestrus period, a consequence of poor nutrition and suckling management.

• Conception rate was poor probably due to poor heat detection, inappropriate timing of AI or poor semen quality.

• Gestation length compared favourably to values reported by other workers for the same breed.

• Calf birth weight was affected by sex of calf, with male calves having higher weights than female calves.

Acknowlegement 

Mr. Abdulai Mammah, Ebenezer Dodd, Stephen Xeflide and Mr. David Charway for their technical advice and recording of data for this work.

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Received 20 August 2008; Accepted 4 September 2008; Published 5 December 2008

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