Enteric methane emissions of grazing short-horn zebu weaner bulls vary with estimation method and level of crude protein supplementation.

Low nutrient intake of short-horn zebu (SHZ) cattle raised under extensive grazing systems results in delayed attainment of mature market weights and consequently increased methane production over time. The purpose of this study was to evaluate and compare the effect of providing grazing SHZ weaner bulls with a supplement varying in crude protein on methane emission using the Intergovernmental Panel on Climate Change (IPCC) Tier 2 and a modified Tier 3 approaches. Weaner bulls were allocated to four treatments: grazing only (GZ), grazing plus a supplement containing either 90 (GZS_90), 110 (GZS_110), or 130 g CP/kg DM (GZS_130). Across treatments, monthly CH4 emissions increased with time. Based on the IPCC Tier 2 method, the highest CH4 production from cattle was estimated from weaner bulls on GZ, while the Tier 3 estimated the highest CH4 production to be from cattle on GZS_130. Although the Tier 2 approach showed no significant difference between treatments, the Tier 3 showed that weaner bulls raised under GZS_130 had the highest production of methane as percentage of gross energy intake. Irrespective of method, weaner bulls on GZ produced more (P < 0.001) CH4 per kilogram live weight gain than supplemented cattle. Compared with Tier 3, the Tier 2 estimated 22.9% higher CH4 per kilogram live weight gain for weaner bulls on GZ. These data suggest that supplementing SHZ weaner bulls with a supplement containing110 g CP/kg DM reduces methane emission per kilogram of live weight gain by 30.7%.

Variability in body weight and morphology of Uganda's indigenous goat breeds across agroecological zones.

Indigenous goat breeds in Uganda are classified based on average body size parameters and coat color. However, variations in the body size of animals may be influenced by several factors, including management and the environment. To understand the effect of the agroecological zone on the physical characteristics and live weight of Uganda's indigenous goats, this study evaluated the body size characteristics of the three indigenous goat breeds of Uganda across ten agroecological zones. The cross-sectional survey was conducted in 323 households from the ten zones, where 1020 goats composed of three breeds (Mubende, Kigezi, and Small East African) were sampled and measured for body weight, linear body size, and age. We confirmed that Mubende and Kigezi goats from the original homeland had a higher mean body weight than reported in FAO reports. In addition, Mubende appeared to perform better in pastoral rangelands, with a higher mean body weight (38.1 kg) and body size being significantly higher (P < 0.0001) compared to other zones. The mean body weight for the Kigezi breed in the original homeland (34 kg) was comparable to those from Western Savannah grasslands and pastoral rangelands and less than that initially reported by FAO (30 kg). Similarly, there was no significant difference in the linear body size characteristics of Kigezi goats in the home zone of highland ranges relative to those found in other agroecological zones (P > 0.05). Although the Small East African goats were originally found in Northwestern Savannah grassland and Northeastern dryland zones, they performed poorly regarding mean body weight and body size characteristics in the former zone. In the Northwestern Savannah grasslands, the mean body weight (23.8 kg) was even less than that reported by FAO, which ranged between 25 and 30 kg. Finally, we confirmed that Mubende and Kigezi goats are significantly heavier than small East African goats (p ≤ 0.0001). The results of this study can be useful in designing precise management strategies to improve indigenous goat productivity in different environments in Uganda.

Genetic diversity, population structure and kinship relationships highlight the environmental influence on Uganda's indigenous goat populations.

Knowledge about genetic diversity and population structure among goat populations is essential for understanding environmental adaptation and fostering efficient utilization, development, and conservation of goat breeds. Uganda's indigenous goats exist in three phenotypic groups: Mubende, Kigezi, and Small East African. However, a limited understanding of their genetic attributes and population structure hinders the development and sustainable utilization of the goats. Using the Goat Illumina 60k chip International Goat Genome Consortium V2, the whole-genome data for 1,021 indigenous goats sourced from 10 agroecological zones in Uganda were analyzed for genetic diversity and population structure. A total of 49,337 (82.6%) single-nucleotide polymorphism markers were aligned to the ARS-1 goat genome and used to assess the genetic diversity, population structure, and kinship relationships of Uganda's indigenous goats. Moderate genetic diversity was observed. The observed and expected heterozygosities were 0.378 and 0.383, the average genetic distance was 0.390, and the average minor allele frequency was 0.30. The average inbreeding coefficient (Fis) was 0.014, and the average fixation index (Fst) was 0.016. Principal component analysis, admixture analysis, and discriminant analysis of principal components grouped the 1,021 goat genotypes into three genetically distinct populations that did not conform to the known phenotypic populations but varied across environmental conditions. Population 1, comprising Mubende (90%) and Kigezi (8.1%) goats, is located in southwest and central Uganda, a warm and humid environment. Population 2, which is 59% Mubende and 49% Small East African goats, is located along the Nile Delta in northwestern Uganda and around the Albertine region, a hot and humid savannah grassland. Population 3, comprising 78.4% Small East African and 21.1% Mubende goats, is found in northeastern to eastern Uganda, a hot and dry Commiphora woodlands. Genetic diversity and population structure information from this study will be a basis for future development, conservation, and sustainable utilization of Uganda's goat genetic resources.