How heat stress (continuous or cyclical) interferes with nutrient digestibility, energy and nitrogen balances and performance in broilers

Abstract

The effect of continuous and cyclical heat stress on broiler growth performance, nutrient digestibility, energy and nitrogen balances was investigated. Four hundred and fifty, 21-day-old, Cobb male broilers were raised in battery cages in five treatments: 22C/AL (continuous 22°C, ad libitum feed consumption); 32C/AL (continuous 32°C, ad libitum feed consumption); 22C/PF32C (continuous 22°C, pair-fed on the daily feed intake of 32C/AL); CY/AL (cyclical-32°C for 8 h and 25°C for 12 h, ad libitum feed consumption); 22C/PFCY (continuous 22°C, pair-fed on the daily feed intake of CY/AL). Between 39 and 42 days of age, dry matter, crude protein, crude fat and AME n were analyzed in the diets and excreta to determine nutrient digestibility. Energy and nitrogen balances were evaluated through comparative slaughter (21 and 42 days of age). Growth performance was significantly lower in broilers exposed to either continuous or cyclical heat stress. However, the cyclical heat stress had a lower effect on feed intake and weight gain and no effect on the feed conversion rate. Nutrient digestibility was only influenced by continuous heat exposure, decreasing dry matter (3.9%) and protein digestibility (9.7%) in comparison to control birds. Broilers exposed to continuous heat stress increased metabolizable energy intake (20.3%) and heat production (35.5%), and decreased energy retention (20.9%) and energy efficiency (32.4%) in relation to control ones. Nitrogen intake and nitrogen retention were reduced by both forms of heat exposure, in comparison to control, but more strongly under continuous heat. Nitrogen retention was reduced by 50.4% and 20.4%, for continuous or cyclical heat stress, respectively. Nitrogen efficiency was reduced only by the continuous heat exposure (33.1%). These results revealed important differences between the effects of a continuous or a cyclical heat exposure in broiler chickens for digestibility, performance and energy and nitrogen balances.

Productive, physiological and immunological responses of two broiler strains fed different dietary regimens and exposed to heat stress

“…Broilers exposed to continuous heat stress increased ME intake (20.3%) and heat production (35.5%), and decreased ME retention (20.9%), ME efficiency (32.4%), nitrogen intake, nitrogen retention (50.4%) and nitrogen efficiency (33.1%) compared to controls. This indicates that a continuous HS had a stronger adverse effect than cyclical ones, which has a less effect on performance and digestibility of nutrients (Souza et al 2016).…”

“…Nonetheless, the influence of HS in the utilisation of ME still requires further verification, as different authors have found an elevation (Keshavarz and Fuller 1980), a decline (Yamazaki and Zi-Yi 1982;Souza et al 2016;Attia and Hassan 2017) and no influence (Geraert et al 1992;Faria Filho et al 2007). Additionally, HS influences meat yield, carcase composition, and ME, independently of feed intake (Cahaner et al 1995;Geraert et al 1996;Attia and Hassan 2017).…”

“…Additionally, HS influences meat yield, carcase composition, and ME, independently of feed intake (Cahaner et al 1995;Geraert et al 1996;Attia and Hassan 2017). Protein metabolism has also been found to be affected by a decline in nitrogen consumption and nitrogen retention (Temim et al 1999;Souza et al 2016). Moreover, a reduction in the deposition of protein in muscle in chickens exposed to HS has been reported (Temim et al 2000;Attia and Hassan 2017).…”

“…In addition, respiratory system and cardiovascular development are negatively affected by high ambient temperature, which causes low performance (Yahav 2000;Steiner et al 2008). Losses in productivity of broilers caused by continuous heat exposure could be explained by the decrease in nutrients digestibility (Bonnet et al 1997;Souza et al 2016) that may be caused by peripheral vasodilation and reduced blood flow in the gut and thus decreased intestinal function (Yamauchi 2002;Attia and Hassan 2017).…”

“…Breakdown and synthesis of protein are adversely influenced by heat stress (Lin et al 2006) and was found to result in low-protein deposition (Temim et al 2000). Heat stress decreased consumption of feeds and digestibility of dry matter and protein, and thus growth, but did not affect FCR (Souza et al 2016). Broilers exposed to continuous heat stress increased ME intake (20.3%) and heat production (35.5%), and decreased ME retention (20.9%), ME efficiency (32.4%), nitrogen intake, nitrogen retention (50.4%) and nitrogen efficiency (33.1%) compared to controls.…”