Effects of rice straw versus wheat straw as ingredients in a total mixed ration on intake, digestibility and growth of Holstein heifers

Abstract

Rice straw (RS) has generally not been considered as an ingredient in dairy heifer or cow rations in the developed world, at least partly due to its tough physical character. However, recent research aimed at developing harvesting methods that increase mixability and reduce animal-sorting problems has identified straw-preparation methods with substantially improved physical properties. A ‘slicer’ baler method was used to prepare RS for use in two feeding studies, so as to determine effects of RS versus wheat straw (WS) as ingredients in a total mixed ration (TMR) on dairy heifer performance. The WS-TMR-fed heifers in Experiment 1 had substantially higher frame growth than did RS-TMR-fed heifers, and maintained body condition score, while RS heifers lost body condition score. A main reason for reduced performance with the RS-TMR-fed heifers was at least partly due to reduced DM intake, which may have been due to slower-degrading fibre and/or a higher dietary cation–anion difference (DCAD) of the RS-TMR. However, the large treatment differences may also have been due to compensatory growth in WS-TMR-fed heifers as all heifers had been fed the RS-TMR before initiation of the study. The WS-TMR-fed heifers in Experiment 2 had the same frame growth, but somewhat higher BCS accumulation, than did RS-TMR-fed heifers, which may have been due to the lower straw-inclusion levels in the diets, smaller treatment differences in DCAD versus Experiment 1 and/or a lack of compensatory growth, since all heifers had been fed a higher-energy diet before the study. However, after a further 28-day period, when all calves were fed the WS-TMR, measures of skeletal growth and BCS had converged. Overall, results support a lower nutritional value of RS than WS, while demonstrating the practical utility of using energy restriction–realimentation regimes to increase heifer growth efficiency.