Growth Performance, Eating Behavior, Digestibility, Blood Metabolites, and Carcass Traits in Growing-Finishing Fat-Tailed Lambs Fed Different Levels of Dietary Neutral Detergent Fiber with High Rumen Undegradable Protein

Hamidreza Mirzaei-Alamouti,Hamid Amanlou,Arman Abdollahi,Jörg R Aschenbach,Amlan Kumar Patra,Azam Beiranvand

doi:10.3390/agriculture11111101

Abstract

This study was conducted to investigate the effect of decreasing concentrations of dietary neutral detergent fiber (NDF) at high rumen undegradable protein (RUP) on performance, digestibility, chewing activity, blood attributes, and carcass characteristics in 32 weaned male Afshari lambs (90 days of age; 26 kg initial body weight; BW). Dietary metabolic energy (ME) was increased from 10.6–11.5 and 11.8 MJ/kg dry matter (DM) by replacing alfalfa hay with grain to achieve NDF concentrations of 270, 245, and 220 g/kg DM, respectively, at 66.6 g/kg DM of RUP. The control (CON) diet contained 10.9 MJ/kg ME, 270 g/kg NDF and 59.6 g/kg RUP on DM basis. Rations containedsimilar concentrations of crude protein (CP, 160 g/kg DM). Lambs were slaughtered after a 56-d feeding period. The increase in dietary RUP had no effect on BW and average daily gain (ADG) but tended to decrease apparent digestibility of CP and DM, significantlydecreasedplasma urea concentration, and increased carcass CP content. Other body or carcass characteristics were unchanged. Decreasing dietary fiber at high RUP did not result in adverse effects on BW, ADG, body length, withers height, apparent digestibility of DM and CP, and BFT, but decreased DM intake (1539 vs. 1706 g/d) and feed conversion ratio (FCR; 4.33 vs. 5.39) compared with CON. Gradual reduction in NDF and physically effective NDF did not affecteating, ruminating or chewing times. Plasma glucose concentration was greater for NDF220 than for the three other treatments (p = 0.015).Slaughtering traits were not affected by dietary treatment except for hot carcass weight, which increased in NDF220 and NDF245 compared with NDF270 (p = 0.021). The concentration of meat CP increased in NDF270 versus CON (167 vs. 152 g/kg). Quadratic effects occurred for meat ether extract concentration (highest in NDF220) and fat-tail weight (highest in NDF245). In conclusion, the results showed that increasing the proportion of RUP within dietary CP improves carcass protein accretion. Decreasing dietary NDF to 220 g/kg DM at high RUP does not impair eating behavior and improves FCR in 3-month-old fat-tailed lambs.

Highlights

Finishing lambs are important meat-producing animals in many regions of the world, providing a major source of protein
The lower DMI observed for lambs fed with NDF220 penetrated to lower overall feed conversion ratio (FCR) (4.33), irrespective of the fact that lowest period FCR was observed for NDF245 in the first 14-d trial period
The present study identified that increasing the proportion of rumen undegradable protein (RUP) within dietary crude protein (CP) has no effect on growth performance but leads to decreased plasma urea concentrations and increased carcass protein concentration

Summary

Introduction

Finishing lambs are important meat-producing animals in many regions of the world, providing a major source of protein. None of the existing feeding standards or models reports optimal dietary fiber (NDF) concentrations for sheep. It is difficult to translate energy requirements into a practical formulation of diets, considering that rumen function and microbial efficiency are markedly affected by fiber nutrients. This is a major limitation, especially for weaned lambs considering their incomplete rumen development, just emerging adaptation to solid feeds, and immature rumination behavior. Fiber-rich diets may profoundly impact DMI and rumen function of weaned lambs with consequences for energy and protein accretion and, growth. Excess starch fermented in the rumen might cause suboptimal rumen pH and associated nutritional disorders [5,6,7]

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Results

Discussion

Conclusion