Nutritional status of Tswana sheep: evaluation of feeding practices and prospects of utilizing protein sources to improve performance

Abstract

This study was conducted 1) to identify the main feed resources and feeding methods used by small-holder sheep farmers; 2) to determine the nutritional and health status of sheep grazing in communal rangelands and 3) to determine the best cost effective protein source to use for market lambs as a replacement for soybean meal (SBM). The study evaluated the nutrient intake, digestibility, utilization, blood metabolites, performance, carcass traits and meat quality of Tswana lambs fed cereal stover-based diets containing increasing levels of canola meal (CM) and sunflower seed cake (SSC). It was postulated that the growth rate, reproduction performance and immunity level of communal sheep were significantly affected by insufficient nutrient supply from the rangelands. To investigate this, an analysis of herbaceous biomass yield and quality as well as the nutritional status of grazing sheep was conducted across all four (4) districts in Southern and Gaborone agricultural regions of Botswana. Additionally, it was presumed that higher levels of CM or SSC could have a negative impact on feed utilization, growth performance, carcass yield and quality as well as the overall health status of Tswana sheep lambs.

It was determined that feed supply and quality in the investigated communal rangelands were inadequate to sustain sheep production during dry seasons and this might have been exacerbated by their high bush encroachment (canopy cover at 70.63%). Most of small holder farmers utilized crop residues (67%) and lucerne/lablab hays (51%) in feeding their sheep and very few supplement their animals with oilseed meals. This study also evaluated the herbaceous yield and nutritional status of communal rangelands and found that the South East and Southern districts had significantly (P<0.05) lowest and highest feed supply respectively. Hence, sheep in the South East district had the statistically lowest live body weights and BCS in this work and may reflect their low total nutrients intake. Furthermore, the assessment of blood metabolites of sheep in the South East district indicated intense mobilization of protein and energy reserves, probably due to extended feed scarcity and inadequate nutrients consumption during the dry seasons. Sheep from the South East district revealed highest (P<0.05) values of creatinine, BUN, glucose and cholesterol and these are mostly associated with severe hypoproteinamia and hypoglycaemia conditions.

Again, the current study revealed that the nutritional and health status of grazing sheep was affected by their physiological status, with poor (P<0.05) BCS in lactating ewes. It must be noted that these low nutritional parameters in herbaceous forages and grazing sheep validate the importance of supplementing communal animals, especially with oilseed meals during the dry seasons.Again, this study presumed that increasing levels of CM or SSC would negatively affect feed utilization, growth performance, carcass yield and quality and health status of this dominant sheep breed amongst local small-holder farmers. Thirty-six (36) castrated Tswana sheep weaners were randomly allocated nine (9) isonitrogenous (14% CP) diets in a completely randomized design (CRD) with four (4) animals as replicates. The SBM in experimental diets was substituted by CM or SCC at 0 (control), 25 (CM25/SSC25), 50 (CM50/SCC50), 75 (CM75/SCC75) and 100% DM(CM100/SCC100) inclusion levels and the best replacement rates of SBM were determined. Nutrient intakes and in-vivo digestibility of diets were affected (P<0.05) by inclusion rate of CM or SCC. Higher (P<0.05) intakes of dry matter (DM) and organic matter (OM) were observed in weaners that were fed CM75 and SCC75, while all diets had similar (p>0.05) crude protein digestibility. The results also showed that diets significantly (P<0.05) affected weight gains of lambs but did not affect (P>0.05) their final body weights, feed intakes, FCR and BCS. Even though CM and SCC influenced all investigated parameters similarly (P>0.05), CM produced numerically higher values of growth performance in Tswana sheep lambs. Regarding nitrogen utilization, it was found that diets affected (P<0.05) N-intake, weights of excreta (feces and urine) and daily output of fecal nitrogen while daily weights of urine nitrogen, nitrogen balance and retention were not affected. N-intake followed the pattern for total feed intake, DMI and CPI where it was higher (P<0.05) in sheep weaners fed diet SSC75 when compared to those fed diets SSC25 and SCC50 (32.25 vs 28.99 and 28.14 g/ day). Also, fecal output was inversely related to ADF, DMD and OMD levels of the investigated diets and it was significantly higher for sheep fed diets with high inclusions of CM, CM75 (1.02 kg) and CM100 (0.98 kg). Furthermore, all diets resulted in similar concentration levels of blood metabolites (except urea), normal levels of creatinine, total protein, Ca (except SSC100) and P and below normal levels of urea and albumin in Tswana lambs.

Once more, it was observed that all the diets had a significant influence (P<0.05) on various parameters including hot carcass weight (HCW), cold carcass mass (CCM), percentage of meat shrinkage, bone percentage, as well as the weights of ribeye, neck, rib-chop, leg, chump, loin, and rib-flank of the lambs. Animals fed control diet had significantly higher values of HCW and CDM than those that were fed diets SSC25 and SSC100. Furthermore, all CM and SSC diets, except SSC25, produced non-significant weights of rib-chop, leg, chump, loin and rib-cuts to control diet. The current findings also revealed that substituting SBM with CM or SSC affected the levels of drip loss, cooking loss and tenderness. Lamb meat with the highest drip loss percentage and lowest values of tenderness and highest fat and lowest moisture contents was produced by control and CM100 and SSC100 and SSC75 diets, respectively. Sensory evaluation scores indicated that replacing SBM with CM or SSC significantly affected all investigated sensory attributes of meat except taste and flavour, with higher (P<0.05) scores on tenderness, juiciness and overall impression in meat of lambs fed diet SCC75 than that of lambs fed control diet. From the results, it is concluded that CM or SSC has potential to partially or wholly replace SBM in grower sheep diets and feeding indigenous sheep improved cereal crop residues-based diets with CM or SCC has high chances of increasing mutton meat supply and consumption in hot and dry climates of Africa. A situation of high availability and affordability of animal protein has a high potential of reducing prevalence of undernourishment in the continent.