Optimising Breeding Strategies Incorporating Resistance to Gastointestinal Helminths in Meat Sheep in Kenya

Abstract

Sheep diseases and parasites, especially Gastro-intestinal (til) helminths are major constraints to improved productivity. A cheaper and more sustainable strategy to controlling (ll helminths is to exploit the inherent resistance to G] helminths in sheep by incorporating this attribute in the breeding objective. 'l'his study therefore aimed at optimising breeding strategies that incorporate resistance to (ll helminths (RES) in meat shccp. A deterministic approach was used to genetically and economically evaluate the efficiency of live two-tier nucleus breeding systems for monetary genetic gain and profitability. These systems differed in whether one was closed or open, in the type ol_' animals that were involved in the movement oti genetic superiority and in the number of selection groups in each system. The systems were compared under tour alternative breeding objectives. The first and second objectives respectively assumed that flock size cannot be increased due to Nonwleed related constraints (l7l.(,)C|§) and that tlocl\ size is restricted due to limited teed resources (l*lilil)) while the third and fourth respectively assumed that sheep perlormed only tangible roles (TR) and both tangible and intangible roles (lR). Economic values for RES were estimated under different scenarios based on previously published genetic and phcnotypic parameters in tt selection index objectively optimising gains on yearling weight. These economic values were used to evaluate the elticiency ol schemes breeding lor RES. 'l'he open nucleus breeding system with commercial aborn ewes being introduced in the nucleus had the highest annual genetic gain under all breeding objectives (i.e., l\’Sh 46.11, 124.8‘), 209.27 and 10.5.31 in l‘l.t )tTl§, l*l£l;'l), ‘l‘R and IR, respectively) but profitability was highest under l~'l.()til\' ( 7 £4 I"/(1.02) and IR (KSh h42.7t)). ln the closed nucleus breeding system that utilised young rams, annual genctic gains were (K511) 43.60, ll7.57, 196.88 and 153.89 in k‘l.O(‘k., l3Elil), TR and IR, respectively. The corresponding profits per ewe were (KSh) l'/5.64, ~'|‘)5.o7, 818.08 and (118.85. ‘l'he annual monetary genetic gain and profit per ewe were highest for the breeding scheme with the highest level of recording (scheme -’l). ln all objectives, the difference in the profit per ewe between a scheme that included records on laecal egg count (l*l1t') measured once in rams immediately alter weaning (scheme 3) and another (scheme »l) that included a second l*l£L‘ measured at 7.5 months was small (l.3 to 3.7%), indicating that there is little benefit taking a second measurement of l*'l"l(l The results suggest that no breeding system is universal. Based on profitability, the optimal nucleus breeding system changes with the breeding objective and incorporating RES in the breeding objective always result in higher returns and profitability. Successful establishment of any nucleus breeding system or scheme should therefore focus on the logistics of establishing them.