Energy requirements and efficiency of energy utilization in growing dairy goats of different sexes

Abstract

The aim of this study was to investigate the effects of sex on the requirements for maintenance and efficiency of energy utilization in growing Saanen goats. A database from 7 comparative slaughter studies that included 238 Saanen goats was gathered to provide information for the development of prediction equations of energy requirements for maintenance and efficiency of energy utilization. The experimental design provided different levels of metabolizable energy intake (MEI) and empty body weight (EBW). The data were analyzed so that sex (e.g., intact males, castrated males, and females; n = 98, 80, and 60, respectively) was a fixed effect, and blocks nested in the studies and goat sex were random effects. For the development of linear and nonlinear equations, we used the MIXED and NLMIXED procedures in SAS (SAS Institute Inc., Cary, NC). Nonlinear regression equations were developed to predict heat production (HP, kcal/kg 0.75 of EBW; dependent variable) from MEI (kcal/kg 0.75 of EBW; independent variable). Using the comparative slaughter technique, the net energy requirement for maintenance (NE M ) was calculated as the value of HP at MEI equal to zero. Additionally, NE M was evaluated based on the degree of maturity. The metabolizable energy requirement for maintenance was calculated as the value at which HP is equal to MEI. Efficiency of ME utilization for maintenance (k m ) was calculated as the ratio between NE M and the metabolizable energy requirement for maintenance. Efficiency of energy utilization for growth (k g ) was assumed to be the slope of the linear regression of retained energy (RE) on MEI above the maintenance stage (model intercept equal to 0). Efficiencies of RE as protein (k p ) and as fat (k f ) were calculated using the multiple linear regression of MEI above the maintenance (model intercept equal to 0) on RE as protein and as fat, respectively. Sex affected NE M (75.0 ± 1.76 kcal/kg 0.75 of EBW for males and 63.6 ± 2.89 kcal/ kg 0.75 of EBW for females) and sex did not affect k m (0.63). In contrast, sex no longer affected NE M when degree of maturity was considered on its estimation. The k g was different between sexes (0.31 for castrated males and females, and 0.26 for intact males), but k p (0.21) and k f (0.80) were similar between sexes. These results may be useful for improving robustness of the energy requirement recommendations for dairy goats.

Body weight and sex effects on digesta mean retention time in growing Saanen goats

“…In the offered diet and orts, the dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), and indigestible NDF (iNDF) concentration were determined, and posteriorly intake of DM (DMI), OM (OMI), NDF (NDFI), iNDF (iNDFI), potentially degradable NDF (pdNDFI) were calculated. In addition, we calculated the feeding level as multiples of metabolizable energy (ME) requirements for maintenance intake (L), using ME requirements for maintenance of growing Saanen goats ( Souza et al, 2020 ). The ME in the diet was estimated when goats were around 22 and 37 kg BW for study ( Leite et al, 2015a , 2015b ) and ( Silva, 2013 ), respectively.…”

“…The ME concentration in the diet (kcal/kg of DM) was estimated from gross energy intake, total energy losses from feces, urine, and gaseous products of digestion. Fecal and urinary excretions were obtained from their total collection ( Souza et al, 2020 ). Energy loss from gaseous products of digestion was predicted according to Blaxter and Clapperton (1965) equation, as described by Souza et al (2020) .…”

“…Fecal and urinary excretions were obtained from their total collection ( Souza et al, 2020 ). Energy loss from gaseous products of digestion was predicted according to Blaxter and Clapperton (1965) equation, as described by Souza et al (2020) . The feed intake was expressed as g and % of BW.…”

“…Feed intake and ingested feed are considered the driving force of MRT, and both are dependent on energy requirements ( Clauss et al, 2007b ; Meyer et al, 2010 ; Souza et al, 2017 ; Müller et al, 2013 ). In addition, recent meta-analytical studies with growing Saanen goats have shown sex and BW effects on net energy requirements for maintenance and growth ( Souza et al, 2017 ; Souza et al, 2020 ). Therefore, considering a possible BW and sex effect on MRT, and the lack of studies with Saanen goats, the aim of this study was to evaluate the effects of BW and sex on MRT of particles and solutes in Saanen goats throughout the growing phase.…”

Genotype effects on energy and protein requirements in growing male goats

“…Previous studies showed that sex (Souza et al, 2017) and breed (Taylor, 1980) differences in body composition at the same BW shrink when comparing animals at the same degree of maturity. Likewise, methods to overcome genotype effect due to differences in maturity degree on nutritional requirements have been applied (Souza et al, 2020) while considering the comparative slaughter technique. In this sense, Emmans (1989) suggested to describe and evaluate different genotypes using potential protein growth, enabling the identification of genotypic differences in energy content.…”