A deterministic approach was used to genetically and economically evaluate the efficiency of five two-tier nucleus breeding systems for meat sheep in Kenya. The nucleus breeding systems differed in terms of whether the system was closed or open, in the type of animals that were involved in the movement of genetic superiority and in the number of selection pathways in each system. These systems were compared under four alternative breeding objectives based on monetary genetic gain and profit per ewe. The first objective simulated a situation where the flock size cannot be increased due to non-feed related constraints (FLOCK). The second specifically assumed that the flock size is restricted due to limited amount of feed resources (FEED). The third and fourth objectives assumed that sheep performed only tangible roles (TR) and both tangible and intangible roles (IR) in the production system respectively. Monetary genetic gains were highest for all objectives in an open nucleus system with a certain proportion of commercial-born ewes being introduced in the nucleus while at the same time utilizing young rams from the nucleus to breed sires and dams for the nucleus and commercial sector (ONyre). Utilizing young rams in a closed nucleus system for the dissemination of superior genes resulted in higher annual monetary genetic gain than utilization of old rams. Profit per ewe was significantly higher for FLOCK and IR in ONyre. In a closed system that allowed for downward movement of dams from the nucleus to the commercial sector to breed sires and dams, profit per ewe was highest for FEED and TR. The success of a nucleus breeding system should also focus on the profitability and logistics of establishing it. The implication of these results on the choice of two-tier nucleus breeding systems for the improvement of meat sheep is discussed.

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Economic values for resistance to gastrointestinal (GI) helminths in meat sheep were estimated based on previously published genetic and phenotypic parameters in a selection index objectively optimizing gains on yearling weight (YW). A two-trait index of YW and faecal egg count (FEC) were considered when accounting only for tangible roles of sheep production using individual records for index calculation (scheme 1) or including individual, sire, dam and male paternal half-sib information (scheme 2). Schemes 3 and 4 were similar to schemes 1 and 2, respectively, but accounted for both tangible and intangible roles of sheep production. Economic values within each scheme were estimated for five breeding objectives as follows: (i) index response in YW equals response from single trait selection, (ii) index response in YW is maximum, (iii) the level of FEC was held constant, (iv) A predetermined response of -0.22 (x1000) eggs per gram was assumed and (v) Monetary value of response in FEC is minimum. All estimated economic values were negative, and were Kenya Shillings (KSh) -34.90 (US dollar -0.50), 0.00, -92.20 (US dollar -1.32), -153.31 (US dollar -2.19) and -47.90 (US dollar -0.68), respectively, for options 1-5 in scheme 1. In all schemes the breeding options ranked 4, 3, 5 and 1 in descending order; however, options 1 and 5 exchanged positions in schemes 2 and 4. Economic values were responsive to changes in heritability of FEC and genetic correlation between the two traits. The magnitude of the economic values reflects the importance of including resistance to GI helminths in the breeding objectives for meat sheep in different production systems.

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The chemical composition and in situ dry matter (DM) and organic matter (OM) degradability of seven different cereal crop residues were evaluated in this study.They included the Sorghum stovers (SS) and its threshed head residues (STH), millet stovers (MS) and its threshed head residues (MTH), corn stover (CS), wheat (WS) and barley (BS) straws. A legume crop residue (lentil, Lens esculanta, straw; LS) was included for comparison with the cereal crop residues. The CS was high (P < 0.05) in crude protein (CP) and acid detergent lignin (ADL) and the lowest (P < 0.05) in Neutral Detergent Fibre (NDF) and acid detergent fibre (ADF) when compared to the amounts in SS and MS. It was found out that LS had higher (P < 0.05) CP, ADL, ME and low (P < 0.05) NDF and ADF than the cereal crop residues. There were differences in digestible DM (DMD) at various incubation times both between and within the feed samples. The DM and OM a, c fraction were highest (P < 0.05) for LS when compared to all the cop residues evaluated. The BS and MS had the lowest effective degradability (ED) DM at 0.02 and 0.05 (P < 0.05) rates of passage, while the LS had the highest. The chemical composition and degradability of different crop residues found in Eritrea indicate the potential the residues have in supplementing grazing animals.

This study was carried out to determine the chemical composition and in situ degradability of agro-industrial by-products found in Eritrea. Three categories of byproducts were evaluated and were the milling industry (wheat bran; WB, short; WS, and middling; WM), brewery (brewers' dry grain; BDG, hops; BDH, and yeast; BDY) and sesame cakes (sesame cake machine extracted; SCM and manually extracted; SCT). The dry matter (DM) varied between 88.46% in BDY to 92.39% in SCT. The lowest (P < 0.05) crude protein (CP) content was recorded in WM at 10.11% while the highest was from the BDY at 48.20%. The metabolisable energy (ME) value of the agro-industrial by-products ranged from 8.72 to 11.18 MJ per kg DM with the BDH recording the lowest value (P < 0.05). The sesame cakes (SCM and SCT) recorded higher values of 11.17 and 11.18 MJ per kg DM respectively. The SCT recorded the highest ash content at 10.93% followed by BDY at 10.16% with the least being obtained from WM at 2.48%. The ether extract and acid detergent lignin contents were generally low in all cases for all the by-products. Generally, the results indicated that there was no clear pattern in terms of nutrients content amongst the by-products.The in situ DM, organic matter (OM) and CP degradability differed amongst and within the sesame cakes, milling and brewery by-products. The wide variation in chemical composition, DM, OM, CP degradability, and ME obtained from this study offer farmers huge flexibility in formulating rations according to the productive performance of target animals.

Farm profitability is the key driver of most livestock enterprises. The productivity and profitability are driven by genetic potential of the animals and the ability to express the superiority in the production environment. In an ideal situation, an animal should produce maximally as dictated by the genetic potential. It is noteworthy that the environment in which an animal lives in impacts on its ability to expose its genetic potential. Studies have shown that it is rarely feasible to provide animals with ideal conditions to express their full genetic potential. The environment in which animals are reared is characterised by many factors that interact in ways that result in different performance even in animals of similar genetic makeup. For instance, thermal environment is critical in poultry production as it affects both the production and reproduction in different ways. The thermal environment affects chicken differently depending on the stage of growth or production phase. This environment has been impacted by the climate change and subsequent increase in climatic variability resulting in thermal challenges in naturally produced chicken thus altering production and reproduction. This implies that there is need to consider thermal resource in the routine poultry management practices. This would result to design of poultry production systems responsive to the thermal environments more so in the light of climate change and the subsequent increase in climatic variability. This chapter explores the impact of heat stress on chicken production, reproduction, health and its dietary amelioration.