The assessment of the presence of genotype by environment interaction (GxE) in beef cattle is very important in tropical countries with diverse climatic conditions and production systems. The present study aimed to assess the presence of GxE by using different reaction norm models for eleven traits related to growth, reproduction, and visual score in Nellore cattle. We studied five reaction norm models (RNM), fitting a linear model considering homoscedastic residual variance (RNM_homo), and four models considering heteroskedasticity, being linear (RNM_hete), quadratic (RNM_quad), linear spline (RNM_l-l), and quadratic spline (RNM_q-q). There was the presence of GxE for age at first calving (AFC), scrotal circumference (SC), weaning to yearling weight gain (WYG), and yearling weight (YW). The best models were RNM_l-l for YW and RNM_q-q for AFC, SC, and WYG. The heritability estimates for RNM_l-l ranged from 0.07 to 0.20, 0.42 to 0.61, 0.24 to 0.42, and 0.47 to 0.63 for AFC, SC, WYG, and YW, respectively. The heteroskedasticity in reaction norm models improves the assessment of the presence of GxE for YW, WYG, AFC, and SC. Additionally, the trajectories of reaction norms for these traits seem to be affected by a non-linear component, and selecting robust animals for these traits is an alternative to increase production and reduce environmental sensitivity.

The effects of increasing levels of protein supplementation (50, 100, 150 and 200 animal per day) and mineral salt on feed intake, nutrient digestibility and ingestive behavior of sheep consuming tropical forage (Pennisetum purpureum Schum) were evaluated. Five non-castrated crossbred lambs (1/2 Santa Ines x 1/2 undefined breed) with average initial body weight of 35.0 kg (+/- 4.40 kg) were allocated in individual cages and analyzed in a 5x5 Latin square experimental design composed of five animals, five treatments and five evaluation periods of 14 days each. The contrast (protein supplement vs. mineral mixture) was not significant (p>0.05) for total dry matter intake, total organic matter intake, total ether extract intake and total carbohydrate intake variables. However, it was significant (p<0.05) for the variables forage dry matter intake, total crude protein intake, total mineral matter intake, total neutral detergent fiber intake and total non-fibrous carbohydrate intake, demonstrating possible replacement of forage by the supplement. Although the diet dry matter digestibility declined linearly (p <0.05), there was a significant linear increase effect of supplementation (P <0.05) on apparent digestibility of neutral detergent fiber, non-fibrous carbohydrates and consumption of digestible non-fibrous carbohydrates. This was due to higher participation of supplement in the diet ingested by supplemented sheep. The type of supplementation (protein or mineral mixture) did not affect the animals' daily activities. Protein supplementation did not affect the water ingestion (P 0.05) either the water intake or ingestive behavior of sheep, with rumination and rest coinciding with dusk and dawn.