This study investigated the influence of non-genetic factors on reproductive performance of Boran cows and heifers reared under ranch conditions in Tanzania. Data on reproduction performance were collected from Kikulula Heifer Breeding Unit (KHBU) in northwestern Tanzania. Reproductive traits studied were age at first calving (AFC), calving interval (CI), days open (DO) and number of services per conception (NSC). General Linear Models (GLM) procedure of Statistical Analysis System (SAS) was used for data analyses. The overall means for AFC, CI and DO were 42.2±0.23 months, 463.6±1.93 days and 183.4±1.93 days, respectively. AFC was significantly (P<0.001) influenced by year-season and type of mating whereby heifers and cows bred in the late dry season performed better than those bred in the heavy rain season. Heifers bred by natural service were about 4 months younger at first calving than artificially bred ones. With regard to CI and DO, year-season of mating, type of mating and parity were also important sources of variation. Cows that calved in the heavy rain season had longest CI and DO than those calving in other seasons. The two traits significantly decreased from first to fourth parity and then increased. Artificially bred cows had poorer performance compared to those naturally bred. The overall mean for NSC for both heifers and cows was 1.57±0.01. Parity, year-season of mating and type of mating significantly (P<0.001) affected NSC. Heifers had the highest NSC (1.73) and were decreasing with age till fourth parity. Further, cows and heifers mated in the dry season had significantly more NSC than female cattle mated in the wet season; while artificially bred animals had significantly higher (1.71±0.03) NSC than naturally bred ones (1.53±0.03). From the findings, it is concluded that in order to improve reproductive performance, environmental factors should be accorded more serious consideration.
Reproduction in livestock is crucial for production of the necessary replacement stock, for reducing unproductive periods, for initiation of lactation, for increasing lifetime milk production and income (Das et al., 1986). When the reproductive efficiency of a farm is poor losses that can occur include fewer calves being born due to longer calving intervals, increased veterinary costs due to more problematic cows, increased number of matings to achieve conception as a result of poor heat detection, and increased number of replacement heifers needed for non-voluntary reproductive culls.
In tropical countries, Bos indicus cattle are the predominant species kept by the majority of small holder farmers. These cattle are well adapted to tropical environments. They possess a high degree of heat tolerance; they are fairly resistant to ticks and tick-borne diseases and to many other diseases, and have low nutritional requirements (Cunnigham & Syrstad, 1987). However, these cattle are characterised by high age at first calving, long calving intervals and low potential in terms of growth traits (Rege et al., 2001).
3 MATERIALS AND METHODS
Data used in this study were collected from Kikulula Heifer Breeding Unit (KHBU) in Kagera region, North-western Tanzania. This region lies just below the equator between latitudes 1º 00´ and 2º 45´ south and is west of Lake Victoria.
3.1 Management of animals:
New born calves were left to suckle until weaning at about 4 months of age. Weaned and adult cattle grazed on natural pastures, comprising mainly of Cynodon spp, Panicum spp, Eragrostis spp, and Andropogon spp for about 8 hours per day and were returned to the sleeping paddocks in the afternoon. The length of grazing period depended on season, and it was always longer during the dry season than during the wet season. Animals were occasionally supplemented with rocks made from natural salt (NaCl). Boran heifers and cows were kept into two groups; one comprised of those intended for natural mating by Boran bulls and the other group comprised of those intended to be inseminated with Friesian semen to produce F1 crosses. Heifers joined the mating groups when they were about 15-18 months of age. Detection of heat on cows and heifers to be bred by artificial insemination using Friesian semen was initially done using vasectomised bulls or steers and later by close observation of the heifers and cows early in the morning and late evening by trained staff and herdsmen. Heifers and cows intended to be mated by Boran bulls were also monitored daily by trained staff and herdsmen to detect heat. Dates of mating were recorded daily and pregnancy diagnoses were done routinely in order to determine number of services that led to In an attempt to combat this situation, imported Bos taurus germplasm from temperate countries has been widely used in crossbreeding with Bos indicus cattle in many parts of the tropics in order to improve cattle productivity (Syrstad, 1985). In producing crossbred stock, either exotic bulls or semen from exotic sires has been used on indigenous cows. It is of interest to know which of the two methods of mating is efficient under tropical conditions. The objective of this study was to investigate the factors affecting reproductive performance of Boran cows and heifers bred naturally with Boran bulls and those artificially inseminated with Friesian semen under ranch conditions.
conception. All animals underwent routine disease control measures, especially against tick- borne diseases and worm infestations.
3.2 Data classification:
Seasons of birth or calving were categorized into four classes as heavy rain season (March-May) =1; light rain season (September-December) = 2; early dry season (January-February) = 3; and late dry season (June- August) = 4. Parturition numbers were coded 0 (heifers) to 6. Types of mating were coded as NS and AI for natural mating and artificial insemination, respectively. Data available for age at first calving (AFC) were from 1990-1996, records for calving interval (CI) and days open (DO) were available from 1993-1998 and for number of services per conception data were available from 1993-1999 and 1994-1999 for artificial insemination and natural mating, respectively.
3.3 Data analyses:
Data were analyzed using GLM procedures of SAS (2000). Model I was used to analyze age at first calving (AFC) in which year- season of birth and type of mating were included as fixed effects. Model II was employed in the analyses of calving intervals (CI) and days open (DO) whereby fixed effects of parity, year-season of calving, and type of mating were fitted. In analysing the number of services per conception, fixed effects of year-season of mating, , type of mating and parity were fitted in the model (Model III).