Lamb survival and ewe longevity in a crossbreeding program between indigenous and exotic sheep in semi-arid lands

The survival of lambs and longevity of ewes within flocks are important for the sustainability of sheep populations especially in arid and semi-arid lands (ASAL). In this study we conducted pre- and post-weaning survival analysis of lambs and the longevity of ewes of indigenous pure Red Maasai (RRRR), pure Dorper (DDDD), and their crosses comprising F1 (DDRR) and 75 %Dorper-25 %Red Maasai (DDDR) using Cox and Weibull proportional hazard models. The objective was to determine the genetic and non-genetic factors affecting lamb survival to yearling as well as ewe longevity. Data comprised records on 6313 lambs and 2003 ewes. Overall pre-weaning mortality was lower (5 %) compared to post-weaning mortality rate (17 %). Lambs born during the long dry season had a higher risk of dying than those born during the wet seasons. For both lambs and ewes, the Dorper had the highest risk of dying or being culled. Among the crossbreds, the DDDR lambs and ewes had higher risks of dying or being culled relative to F1 lambs and ewes. The risk of ewes being culled reduced with increasing age at first lambing and parity. Heritability estimates for pre-weaning mortality were higher (0.10–0.14) than post-weaning mortality (0.01–0.05). The higher heritability for pre-weaning lamb survival in indicates greater genetic variation, presenting an opportunity for selection for lamb survival. Interventions to improve the production environment in the ASAL areas would also improve the survival of lambs and longevity of ewes.</p

The effects of severe myopia on the properties of sampling units in peripheral retina

Significance: Poor peripheral visual acuity in myopia may reflect, in part, photoreceptor misalignment with the exit pupil of the eye. We speculate that if such misalignment causes sufficient visual deprivation and/or disrupts retinal feedback processes, it may influence eye growth itself. Purpose: It is known that myopic eyes have a reduced peripheral resolution acuity relative to emmetropic eyes, though it remains unclear how mechanical stretching of the retina in myopia impacts on peripheral visual performance. Our aim was to determine how retinal stretching affects the properties of sampling units in peripheral vision. Methods: Three-dimensional magnetic resonance imaging provided a depiction in vivo of ocular shape, allowing the inter-eye ratio of retinal image surface areas and the relative alignment of surfaces to be determined in our observer, who was unique in having severe myopia in the right eye (~21D) but only modest myopia in the left (~3D). Visual performance was assessed for the detection and direction discrimination of drifting sinusoids positioned 40º in the temporal retina. Applying the sampling theorem to our measures, we estimated the density and cut-off frequency of the underlying sampling units. Results: The retinal image surface area of the right eye was 40% larger than that of the left, and was rotated 8.9º anticlockwise relative to the left eye’s image surface. In agreement with a linear stretch model of myopia, the sampling density of the right eye was reduced by approximately the same ratio as that predicted from the inter-eye MRI data, namely 1.18. However, the cut-off frequency (cycles/mm) of the right eye was approximately half that of the left, a reduction that cannot be explained solely by a linear areal expansion of retinal sampling units. Conclusions: Poor peripheral acuity in severe myopia may be caused, at least in part, by receptoral misalignment with the exit pupil

Genetic analysis of phenotypic indicators for heat tolerance in crossbred dairy cattle

Climate change-induced rise in global temperatures has intensified heat stress on dairy cattle and is contributing to the generally observed low milk productivity. Selective breeding aimed at enhancing animals’ ability to withstand rising temperatures while maintaining optimal performance is crucial for ensuring future access to dairy products. However, phenotypic indicators of heat tolerance are yet to be effectively factored into the objectives of most selective breeding programs. This study investigated the response of milk production to changing heat load as an indication of heat tolerance and the influence of calving season on this response in multibreed dairy cattle performing in three agroecological zones Kenya. First-parity 7-day average milk yield (65 261 milk records) of 1 739 cows were analyzed. Based on routinely recorded weather data that were accessible online, the Temperature-Humidity Index (THI) was calculated and used as a measure of heat load. THI measurements used represented averages of the same 7-day periods corresponding to each 7-day average milk record. Random regression models, including reaction norm functions, were fitted to derive two resilience indicators: slope of the reaction norm (Slope) and its absolute value (Absolute), reflecting changes in milk yield in response to the varying heat loads (THI 50 and THI 80). The genetic parameters of these indicators were estimated, and their associations with average test-day milk yield were examined. There were no substantial differences in the pattern of milk yield response to heat load between cows calving in dry and wet seasons. Animals with ≤50% Bos taurus genes were the most thermotolerant at extremely high heat load levels. Animals performing in semi-arid environments exhibited the highest heat tolerance capacity. Heritability estimates for these indicators ranged from 0.06 to 0.33 and were mostly significantly different from zero (P &lt; 0.05). Slope at THI 80 had high (0.64–0.71) negative correlations with average daily milk yield, revealing that high-producing cows are more vulnerable to heat stress and vice versa. A high (0.63–0.74) positive correlation was observed between Absolute and average milk yield at THI 80. This implied that low milk-producing cows have a more stable milk production under heat-stress conditions and vice versa. The study demonstrated that the slope of the reaction norms and its absolute value can effectively measure the resilience of crossbred dairy cattle to varying heat load conditions. The implications of these findings are valuable in improving the heat tolerance of livestock species through genetic selection.</p

Genetic Relationships Among Resilience, Fertility and Milk Production Traits in Crossbred Dairy Cows Performing in Sub-Saharan Africa

Change in climate over the past years and its impact on the environment have necessitated the inclusion of resilience traits in the breeding objectives of dairy cattle. However, the relationship between resilience and other traits of economic importance in dairy production is currently not well known. This study examined the genetic parameters and relationships among resilience, fertility and milk production traits in dairy cattle in Kenya. Indicators of general resilience and heat tolerance were defined from the first parity test-day milk yield records. Indicators of general resilience included variance of actual deviations (LnVar1), variance of standardised deviations (LnVar2), lag-1 autocorrelation (rauto) and skewness (Skew) of standardised deviations in milk yield. Heat tolerance indicators at temperature-humidity index 80 included the slope of the reaction norm (Slope), absolute slope of the reaction norm (Absolute), and the intercept of the reaction norm model (Intercept). Cows with &gt; 50% taurine genes had lower age at first calving (AFC), longer calving intervals (CI) and higher test-day milk yield (MY). The heritability estimates of AFC, CI and MY were 0.17 ± 0.033, 0.06 ± 0.012 and 0.35 ± 0.021, respectively. The repeatability estimates of CI and MY were 0.06 ± 0.012 and 0.47 ± 0.009, respectively. The low heritability and non-significant permanent environmental variance of CI showed that CI is heavily influenced by external factors, such as management practices. AFC was negatively genetically correlated with both CI (−0.88 ± 0.077) and MY (−0.53 ± 0.059) showing that animals that attain sexual maturity earlier exhibit longer CI and higher milk production. A positive genetic correlation (0.62 ± 0.077) between CI and MY shows that high-yielding cows face challenges in maintaining shorter calving intervals. Heritability estimates of nearly all resilience indicators were significant and ranged from 0.05 to 0.34. Heat tolerance indicators showed low to non-significant genetic correlations with general resilience indicators, suggesting that different genetic factors are involved in responses to different types of disturbances. There was a generally positive genetic correlation between resilience and fertility, implying that resilient animals might have better fertility. All indicators, except LnVar1 and LnVar2, revealed an antagonistic genetic relationship between resilience and milk production. The findings present an opportunity for including resilience in the development and application of selection indices in dairy cattle, especially for the tropics.</p

Genetic Relationships Among Resilience, Fertility and Milk Production Traits in Crossbred Dairy Cows Performing in Sub-Saharan Africa

Change in climate over the past years and its impact on the environment have necessitated the inclusion of resilience traits in the breeding objectives of dairy cattle. However, the relationship between resilience and other traits of economic importance in dairy production is currently not well known. This study examined the genetic parameters and relationships among resilience, fertility and milk production traits in dairy cattle in Kenya. Indicators of general resilience and heat tolerance were defined from the first parity test-day milk yield records. Indicators of general resilience included variance of actual deviations (LnVar1), variance of standardised deviations (LnVar2), lag-1 autocorrelation (r auto) and skewness (Skew) of standardised deviations in milk yield. Heat tolerance indicators at temperature-humidity index 80 included the slope of the reaction norm (Slope), absolute slope of the reaction norm (Absolute), and the intercept of the reaction norm model (Intercept). Cows with &gt; 50% taurine genes had lower age at first calving (AFC), longer calving intervals (CI) and higher test-day milk yield (MY). The heritability estimates of AFC, CI and MY were 0.17 ± 0.033, 0.06 ± 0.012 and 0.35 ± 0.021, respectively. The repeatability estimates of CI and MY were 0.06 ± 0.012 and 0.47 ± 0.009, respectively. The low heritability and non-significant permanent environmental variance of CI showed that CI is heavily influenced by external factors, such as management practices. AFC was negatively genetically correlated with both CI (−0.88 ± 0.077) and MY (−0.53 ± 0.059) showing that animals that attain sexual maturity earlier exhibit longer CI and higher milk production. A positive genetic correlation (0.62 ± 0.077) between CI and MY shows that high-yielding cows face challenges in maintaining shorter calving intervals. Heritability estimates of nearly all resilience indicators were significant and ranged from 0.05 to 0.34. Heat tolerance indicators showed low to non-significant genetic correlations with general resilience indicators, suggesting that different genetic factors are involved in responses to different types of disturbances. There was a generally positive genetic correlation between resilience and fertility, implying that resilient animals might have better fertility. All indicators, except LnVar1 and LnVar2, revealed an antagonistic genetic relationship between resilience and milk production. The findings present an opportunity for including resilience in the development and application of selection indices in dairy cattle, especially for the tropics.</p

The impact of heat stress on growth and resilience phenotypes of sheep raised in a semi-arid environment of sub-Saharan Africa

Sheep production in Arid and Semi-Arid lands face immense heat stress with the changing climate. This study assessed the effect of heat stress on growth and developed resilience phenotypes of sheep raised in a semi-arid environment. Heat stress was measured by Temperature-Humidity Index (THI). Live body weight records of 4078 animals, belonging to pure Red Maasai (RRRR), pure Dorper (DDDD), and their crosses: 50%Dorper-50%RedMaasai (DDRR) and 75%Dorper-25%Red Maasai (DDDR) collected between 2003 and 2024 were analysed. Random regression models fitted with reaction norm functions were used to develop two resilience phenotypes: Response and Stability, at THI 70 and THI 85 representing varying heat stress. Animal mixed models were used to estimate genetic parameters. The THI breakpoints were 78.75, 78.71, 78.42 and 77.93 with a decline rate of 0.06 Kgs, 0.09 Kgs, 0.05 Kgs and 0.15 in live weight gain per unit change in THI for RRRR, DDDD, DDRR and DDDR respectively. The breed, sex, type of birth, dams’ parity and season of birth significantly (P&lt;0.05) affected the stability of growth at low and high heat stress. The heritability estimates of resilience traits ranged from 0.12 to 0.16. Genetic correlations of resilience phenotypes at THI 85 with pre-weaning live weight gain were antagonistic and significant (P&lt;0.05). With the changing climate, resilience phenotypes should be included in selection programs for sheep in the Arid and Semi-Arid lands for robust growth.</p

The impact of modelling and pooled data on the accuracy of genomic prediction in small holder dairy data

The lack of data recording in smallholder dairy cattle system implies that the availability of molecular data could offer some quick wins in terms of using the genomic information in genomic evaluation and therefore genomic selection (GS). Initial studies have reported low to medium accuracy of genomic prediction when the size of data is limited. The African dairy genetic gains (ADGG) project is generating more data across two countries in East Africa and would offer more opportunity to further examine the application of GS. In anticipation of having more data in future, this paper examined the impact of fitting GBLUP models with dominance effects, a multi-trait GBLUP that fits exotic breed and non-exotic breed proportion as different traits and the analysis of pooled data from Kenya and Tanzania on the accuracy of genomic predictions. In addition, it examines if chromosome regions with highest contributions to top GEBV cows with high exotic and high indigenous genes are different. The estimates of dominance variance were essentially zero, possibly due to the limited data set, and therefore the model with dominance effect resulted in no increase of genomic accuracy compared to a model with only additive effects. The fitting of the proportion of exotic and non-exotic genes as different traits resulted in slightly lower accuracies of cows with more than 35% exotic genes but almost doubled the accuracy of those wit

Current situations of animal data recording, dairy improvement infrastructure, human capacity and strategic issues affecting dairy production in sub-Saharan Africa

An online survey on the state of existing dairy data, dairy improvement infrastructure and human capacity in sub-Saharan Africa (SSA) was undertaken with the aim of assessing whether the state of existing animal recording, dairy improvement methods and key issues facing dairy production together with means of addressing the issues differ among countries and regions of SSA. Respondents comprised experts and practitioners in livestock production and genetic resources from research institutes, animal breeding companies, universities, non-governmental organisations and government agricultural ministries. The main dairy farming system in which the respondents were involved was mixed crop-livestock system (30.2%), and this was mainly practised in the private land tenure system (46.3%). Data were analysed using linear model and paired Student t test in R software package. Respondents identified key issues affecting dairy production as poor genetic assessment of imported exotic breeds and crosses in Africa (62.3%), fluctuations in milk prices within both the formal and informal markets (50.9%), no comprehensive sire ranking systems (39.6%), housing and health management regimes which adversely affect milk yield (32.1%), poor market networks for dairy products (25.5%), poor feeding (13.3%), inadequate genetic technologies (9.4%) and poor animal performance recording systems (9.4%). Respondents emphasised the need for updated breeding policies, sire ranking systems, adequate farm management systems, capacity building, across-country collaborations and joint genetic assessments of dairy breeds found in sub-Saharan Africa. The current situation of dairy production though similar for the different countries, differed in order of emphasis and magnitude across the countries and regions in sub-Saharan Africa.</p