Farming systems in sheep rearing: Impact on growth and reproductive performance, nutrient digestibility, disease incidence and heat stress indices

Abstract

The experiment was conducted with an intent to know the effect of different farming systems on the growth performance, nutrient digestibility coefficients, reproductive traits, disease incidence, heat stress indices, and cost economics of Nellore sheep. The study includes two parallel trials to prevent the influence of age on heat stress indices (panting score and erythrocyte osmotic fragility (EOF)). One hundred and twenty lambs (60 ram-lambs and 60 ewe-lambs) were allotted in a randomized block design under extensive, semi-intensive, and intensive systems for trial I, whereas trial II include eighteen rams assigned to the three respective farming systems in a completely randomised design. Both, season (summer) and grazing practice increased the panting score and EOF. The heat stress indices were positively correlated (P<0.01) with dry-bulb temperature and temperature-humidity index (THI) and inversely correlated (P<0.01) to relative humidity. Allotting the sheep to intensive system increased (P<0.001) weight gain and average daily gain with higher effect in males compared to females. The parameters of asymptotic weight (A), integration constant (B), and maturation rate were higher for intensive males. The male Nellore lambs had higher asymptotic weight and lower maturity rate than females, irrespective of the rearing system. Intensive sheep revealed a higher dry matter intake, digestibility coefficients, feed conversion ratio. The instantaneous bite mass (IBM) was higher for Commelina benghalensis, while instantaneous bite frequency (IBF), instantaneous intake rate (IIR) were higher for Cyanodon dactylon and amaranthus viridis, respectively. The proportion of intakes were highest for Stylo hemata followed by Cynodon dactylon and Tridax procumbens species. No differences were observed for the weight at puberty, oestrus cycle length, oestrus duration, conception percent, gestation period, and lambing percent in three rearing systems; however, the age at puberty was lower (P<0.001) and the birth weight was higher (P<0.001) for sheep reared under intensive farming system. Highest disease incidence was observed in rainy and winter seasons, particularly in sheep reared under extensive system. The capital expenditure was same for the three rearing systems, while the recurring expenditure was higher for Intensive farming system. The gross income and net income were higher for intensive system on account of higher weight gains. However, the higher returns per rupee of expenditure project the extensive farming as an ideal rearing system for small farmers and entrepreneurs with a low initial capital.

Adaptive profiles of Nellore sheep with reference to farming system and season: physiological, hemato-biochemical, hormonal, oxidative-enzymatic and reproductive standpoint

“…The breeding was natural for the ewes with a ram: ewe ratio of 1:20. The methodology adopted along with the results of reproductive parameters were presented in our earlier research ( Karthik et al., 2021 ). In trial II, eighteen rams (S1b File) were allotted in a completely randomized design (CRD) to three treatment groups viz., extensive, semi-intensive, and intensive systems (n = 6).…”

“…The feeding regimen practiced under the three rearing systems is presented in Table 1 while the ingredient and chemical composition of the concentrate mixture fed for semi-intensive and intensive systems are presented in Table 2 . Detailed analysis on the type of browse available in the grazing area is presented in Karthik et al. (2021) .…”

“…The increased pulse rate may augment the blood flow under the body surface, therefore dissipating more heat through conduction, convection, radiation, and water diffusion from skin (Adedeji, 2012;Habibu et al, 2014). The higher pulse rate might result from rapid heartbeat and metabolism due to grazing for long distances (Kochewad et al, 2017). The increased respiratory rate could be attributed to the long walks in semi-intensive and extensive systems (Kochewad et al, 2018a, b).…”

“…The heat stress may precipitate haemoglobin molecules in the erythrocytes, resulting in decreased Hb concentration (Giulivi et al, 1994). Extensive sheep exhibited a decreased PCV percent; however, Kochewad et al (2017) reported a higher PCV in sheep allotted for grazing rather than stall-feeding. The authors attributed the increased PCV to hemo-concentration developed due to asphyxia and dehydration, leading to release of erythrocytes concentrated in spleen.…”

“…The impact of multiple stressors on grazing sheep should be considered, as it is unlikely that sheep will be exposed to a single stressor ( Lees et al., 2019 ). The body weight gains, growth rates, and cost-effectiveness of the sheep under three farming systems are presented in Karthik et al (2021) . The same paper dealt with the heat and nutritional stress instigated by extensive farming system, leading to the lower body weight gains and lesser returns to the shepherds.…”