Bull Mating Load and Its Effects on Conception Outcomes: A Case of TALIRI Mpwapwa Farm

Cattle production underpins livelihoods, food security, and household income in Tanzania, where the improved Mpwapwa breed—developed for high productivity and tropical adaptation—is widely disseminated to upgrade local herds. However, shared communal use often subjects Mpwapwa and crossbred bulls to extreme mating loads of 40 - 60 cows per season, far exceeding temperate-region recommendations, while locally validated guidelines for optimal cow-to-bull ratios remain absent. This study evaluated how mating load, breed, and age influence conception performance using 10 breeding seasons of secondary farm records (2019-2023) from 33 eligible bulls selected from a population of available bulls, each allocated to one of the breeding groups at different mating loads ranging from 1:16 to 1:77, and retained with their assigned groups for the full three-month duration of each breeding season at the Tanzania Livestock Research Institute Mpwapwa station. Data were analyzed via binomial generalized linear models incorporating interaction terms between mating load, breed, and age. Results showed a significant inverse relationship: conception probability declined as dam numbers per bull increased (OR = 0.985, p = 0.001). Mpwapwa bulls were most resilient to higher loads (OR = 1.012, p < 0.0001), while older bulls were more adversely affected (OR = 0.9998, p < 0.0001). The highest conception rates—35.6% for Mpwapwa, 31.2% for Danish Red, and 30.6% for crossbred bulls—occurred at 16 dams per bull, with performance falling sharply beyond this threshold. These findings provide the first empirical breed-specific benchmarks for Tanzania, confirming that universal ratios are unsuitable. Recommended allocations are 16 dams for Mpwapwa bulls, 12 - 14 for exotic and crossbred types, with further reductions for animals over six years old. Adopting these guidelines will preserve fertility, improve reproductive efficiency, and support sustainable genetic improvement across tropical smallholder and research systems.