Improving the performance of Mpwapwa breed cows in Tanzania : a fertility management approach : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, School of Veterinary Science, Manawatu
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2024-12-12
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Massey University
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Abstract
Beef cattle farming is an important part of Tanzania’s economy being widespread throughout Tanzania. It is commonly practiced by small-scale farmers, often in conjunction with other agricultural and commercial activities. As part of the colonial government’s efforts to develop agriculture in Tanzania in the 1940’s, the Mpwapwa breed was developed, largely from Bos indicus stock, as a dual-purpose breed to provide better beef and milk production. The Mpwapwa TALIRI research centre, in the Dodoma region of Tanzania, maintains a nucleus herd of Mpwapwa cattle from which it has provided breeding stock and, prior to 1973, an artificial insemination (AI) program to farmers. These programs fell into abeyance during the post-colonial era. Critically, the AI service was discontinued until TALIRI Mpwapwa started to re-equip its facilities in 2018. The major limiter to re-establishing the AI service has been the high cost and poor availability of liquid nitrogen, which means that it is not feasible to develop a service that is dependent on cryopreserved semen. In the past globally, and in New Zealand currently, bovine AI services have been based upon chilled or ambient temperature (AT) diluents, so the feasibility of developing a new AI service for Mpwapwa cattle using ambient-temperature semen was investigated. Most of the use of AT diluents has been in temperate climates, so an important component of re-establishing the AI service was to determine whether AT diluents could sustain sperm viability at the high (>30oC) temperatures that pertain in Tanzania.
The first step was to survey farmers who kept Mpwapwa cattle about their management and breeding practices using a cross-sectional survey. This was undertaken to determine whether they were interested in an AI program for their cattle and whether they thought it would be a useful method of breeding for their cattle. A survey was administered across 100 farmers in the Mpwapwa region. Median herd size was 7 (range 1-150) and median farm size was 12 acres (0.4-500), milk yields were generally under 5 L/cow/day and carcass weights were typically 112-142 kg. The Mpwapwa breed was regarded as better than other local breeds. Only 17 farmers had used AI, almost always after single-PGF2α synchronisation. However, 69 farmers who had not used AI were interested in doing so and 61 considered that AI was better than natural bull mating being aware of the significant of AI on livestock breeding. The conclusions from the survey were that an AI service would have to be tailored around small herds, probably with fixed-time AI (FTAI) after single-PGF2α synchronisation, and would have to offer farmers significant improvements in animal genetics and fertility and/or easier management of breeding than at the present.
As the Mpwapwa bulls had never been evaluated to determine whether their semen was of adequate quality to use in an AI service, the next step was to undertake breeding soundness examination (BSE) of the bulls in the TALIRI Mpwapwa stud. The 53 heaviest bulls out of the total stud of 120 were subjected to a full BSE including semen examination (collection by electroejaculation). Scrotal circumference was similar in bulls that were 24-36 months old (mean: 27.1 cm, SD: 1.6 cm) and those that were >36 months old (mean: 27.8 cm, SD: 2.0 cm). Semen was successfully collected from 44 bulls. Mean ejaculate volume was 5.5 mL (SD: 2.7 mL). Only 4 bulls did not have ≥75% morphologically normal sperm. Mean ejaculate density was relatively low at 303 x106 sperm/mL (range: 57-966, SD: 258 x106 sperm/mL). Density was >400 x106/mL in 31 bulls, >700 x106/mL in 2 bulls and >800 x106/mL in 6 bulls. These 8 bulls were considered suitable for use in an AI program. The variation of semen quality was largely as expected for a breed that had not been subjected to any form of selection for breeding ability. Findings for these Mpwapwa breed bulls largely align with those of similar low body-weight breeds of B. indicus that are found in East Africa and South-East Asia, but are significantly less than would be expected from the improved indicus breeds of South America, Australia and southern Africa. DNA fragmentation was examined in the same 53 bulls, again, as the status of these hitherto unselected bulls was unknown. Most bulls had unfragmented sperm (mean: 94.7%, SD: 6.8, Mode: 100%), with only 5 bulls having <90% normal sperm. Fragmentation was therefore not sufficiently widespread in the bull stud to cause concern about their use in AI.
The next step was to assess the survival of sperm at ambient temperatures. Ejaculates from 35 bulls were diluted 1:1 in Tris-egg yolk (TE), Optixcell and coconut water, loaded into 0.25 mL mini- straws and incubated in water baths at 20°C, 27°C and 33°C (Year 1) or 8°C, 17°C and 33°C (Year-2). Motility was evaluated using computer-assisted analysis after 6, 24, 48, 72 and 120 h. Sperm survival was related to temperature, such that survival at 8°C was better than at other temperatures. Survival in coconut water was poor, with limited survival even at 24 h. Mean survival at 72 h was <40% in both TE and Optixcell, but was >40% at 48 h except at 32oC. These results suggested that storage at <20oC for up to 48 h would give acceptable motility (i.e. ≥50%) for use in AI. Sperm from some (n=4) individual bulls survived, however, for up to 120 h at 8oC and from 2 bulls at 17oC. Semen from 3 bulls survived for 120 h at 32oC. These results showed that storage for 48 h at 17°C in TE or Optixcell was feasible for most bulls, and individuals could be identified whose semen survived longer and/or at higher temperatures for at least 72 h. Thus, maintaining semen at ambient temperatures of 32°C was difficult for >24 h, but was readily achievable in an AT diluent with a modest amount of cooling for 48 h. This survival would permit an AI service based on AT semen, provided inseminations could be performed soon after collection, or after a period of modest refrigeration.
Finally, a proof-of-concept AI trial was undertaken, in which 303 cows were inseminated with cryopreserved or AT semen after a double-PGF2α synchronisation (to detected oestrus after PGF2α- 1 and by FTAI after PGF2α-2). Conception rates to AI were 62% to AT and 38% to cryopreserved semen (final pregnancy rates were 99% and 97% respectively after 12 weeks of bull mating). Whilst the trial was not undertaken to demonstrate that one method was superior to the other, it did demonstrate that FTAI with AT semen was at least as good as with cryopreserved semen.
In terms of developing an AT AI service, this thesis has shown that it would likely be well-received by smallholder farmers, that there is a cohort of bulls which are of satisfactory breeding quality for use in AI, that their semen survives for long enough for AT semen to be the basis of an AI service, and that results to FTAI are at least as good as with cryopreserved semen. In summary, the protocol itself is cost-effective and, as such, it could be used within the Tanzanian beef cattle breeding programmes. Being simple to schedule should make it easily accessible and implementable by poor smallholder farmers in the Mpwapwa region and, hence more accessible than other expensive protocols with more hormones. Even compared to natural mating, the costs of AT AI are still cheaper, making it more affordable than the costs of buying and managing a high genetic merit Mpwapwa bull. Wider screening of bulls for those whose semen survives longer and/or at higher ambient temperatures would allow for the selection of bulls with the highest quality semen. Addition of a limited degree of refrigeration (maintaining semen at 15-20oC) would allow more flexibility to the AI collection/processing centre.
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Keywords
ambient temperature artificial insemination, oestrus synchronisation programme, bull fertility evaluation, smallholder farmers, Artificial insemination, Tanzania, Mpwapwa, Beef cattle, Breeding, Beef cattle breeds