The Effect of Scrotal Circumference on Pregnancy Rates in Mpwapwa Breed Cattle During September – November 2020 Breeding Season at Taliri Mpwapwa Farm in Tanzania

| The goal of this study was to assess the effect of scrotal circumference (SC) on conception rates in Mpwapwa breed cattle during the Sept – Nov 2020 breeding season. Eight Mpwapwa bulls aged ≥3 years were selected from 23 bulls which had passed a structural soundness and movement tests based on having the largest SC and used to mate 324 non-pregnant Mpwapwa cows. Mating was conducted in eight groups with each group randomly assigned a single bull. For each bull, data were collected on age, pre-breeding body condition score (BCS) and body weight, SC and total number of cows bred. Based on p<0.25 value in a univariable model with pregnancy rate as the outcome variable, all of the variables except bodyweight were included in a multivariable logistic regression model with pregnancy rate as the outcome variable. Of those variables only pre-breeding BCS was clearly associated with odds of pregnancy. Compared to a bull with a BCS of 3.5, a bull with a BCS of 3.0 had only 0.29 times the odds (95% confidence interval (CI) 0.15 to 0.57) of getting a cow pregnant during the breeding season. For SC, the data were compatible with a small decrease and a moderate increase in the odds of pregnancy (odds ratio for a 1 cm increase in SC was 1.05 (95%CI 0.84 to 1.3)). Further research on the association between SC and pregnancy rate in Mpwapwa bulls is needed, including identifying whether there is an interaction between BCS and SC and their effect on subsequent fertility.