Free choice feeding and its impact on feed efficiency and oxidative stress in growing sheep

Abstract

The traditional total mixed ration (TMR) is a staple in the animal feeding industry as it allows, on aggregate, for animals to perform at a high level of efficiency when feeding large numbers of animals together. However, free choice feeding could have performance benefits and help improve the well-being of animals compared to TMR feeding that is used today. With free choice feeding, animals can develop and exercise individual preference of feedstuffs which has been theorized as one potential reason for the improvement in efficiency with free choice feeding. We conducted a study using growing sheep to assess differences in performance and oxidative stress between the two feeding methods. For this study, Polypay lambs (n=23, BW = 29.7 ± 6.6 kg) were utilized with lambs being blocked by body weight and randomly assigned to either a TMR diet (CON) or a free choice diet (FCD). The diets for both TMR and the FCD were of the same primary ingredients, with the free choice group having the macro nutrients (energy and protein) being supplied by the two main components of the TMR, corn and alfalfa, offered separately in pelleted form. For determination of the oxidative health impact of the two feeding systems, blood was collected at the beginning and end of the experiment, and was analyzed for the oxidative stress metabolite malonaldehyde (MDA) and the overall antioxidant capacity (AO). The experiment lasted a total of 42 days. Lambs were fed daily with the refusals targeting 5% to allow for ad libitum consumption. Lambs were weighed weekly for the duration of the experiment and rate of gain was determined using linear regression, with the slope of the regression line being average daily gain (ADG). The heavy block of FCD had a greater (P <0.05) ADG compared to the heavy block of CON (0.23 kg/d vs 0.17 kg/d), but was similar to light blocks of the FCD and CON treatments. For DMI, TDN intake, and the variability of daily intake, there was no significant difference between treatments for any of these variables. For F:G, although no difference was observed between treatments, a significant treatment by block interaction was observed (P = 0.04). Intake of CP was a greater (P = 0.03) for CON than for FCD (0.31 kg/d vs. 0.26 kg/d). Sheep in the FCD group showed an initial preference for the alfalfa pellets, but they began to prefer corn relative to alfalfa as the experiment progressed. Measures of oxidative stress showed no differences between treatment groups at the start as well as the end of the experiment. The results of this study showed that, although some benefits to animal performance might occur with FCD, the positive impact on oxidative stress may not be true in all situations, in contrast with previously published literature.