Production performance, milk composition and cheese quality of crossbred dairy sheep supplemented with dietary omega-3 oils

Abstract

This thesis primarily investigated the effect of supplementing pasture-based dairy sheep with different plant oil-infused and rumen-protected pellets containing eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) on lactation performance, milk and cheese fatty acid composition and cheese eating quality. It was hypothesised that plant oil supplements would interact with sire breed to influence feed intake, body condition score, milk yield and composition, milk and cheese fatty acid contents and sensory attributes of ripened cheese. Sixty Awassi and Awassi × East Friesian crossbred ewes in mid-lactation, balanced by liveweight (59 ± 5.9 kg), milk yield (657 ± 100 g/day), parity (2.8 ± 0.5), and sire breed were randomly allocated into 6 treatment groups of 10 ewes each, that were: (1) supplemented with on-farm existing commercial wheat-based pellets without oil inclusion (control) or supplemented with wheat-based pellets infused with 50 mL/kg dry matter of oils from (2) canola, (3) rice bran, (4) flaxseed, (5) safflower, and (6) rumen-protected EPA + DHA in a 10- week supplementary feeding trial including a 2-week adjustment period. All supplementary diets included the same level of 50 mL/kg DM of oil except for the control group, and all diets were isocaloric and isonitrogenous. Experimental animals were grazed in the same paddock with ad libitum access to pasture, hay, and water. During milking time, each ewe was fed 1 kg/day of the supplemented pellets individually in the milking parlour. Data on weekly body condition score, daily feed intake, feed composition, weekly bulked fresh milk, raw milk, and ripened cheese samples were collected. Feed intake, body condition score, milk yield, milk composition, fatty acid composition of milk and cheese, and cheese sensory attributes were analysed in SAS with sire breed, diet, and week of supplementation and their second-order interactions as fixed effects. It was demonstrated that oil supplementation and sire breed affected animal performance, productivity and quality of milk and its processed product, in that: 1) Rumen-protected oil pellet containing EPA + DHA was the most effective diet that improved milk production, n-3 long-chain (C≥20) polyunsaturated fatty acids (n-3 LC-PUFA) in fresh milk and ripened cheese without any negative effect on animal performance and cheese eating quality. A serving of milk and cheese reached the good and source levels of n-3 LC-PUFA, respectively; 2) Flaxseed oil supplementation elicited not only the highest concentration of α- linolenic acid (ALA, 18:3n-3) in both fresh milk and ripened cheese, but also improved all cheese eating sensory traits. Flaxseed oil also significantly increased n-3 LC-PUFA in milk because a serving of fresh milk met the claimed source of n-3 LC-PUFA; 3) Safflower oil diet considerably improved milk, fat and protein yields. More importantly, this diet also had the most efficiency at enhancing the level of linoleic acid (18:2n-6) in milk and cheese. Safflower oil inclusion had no effect on cheese eating quality; 4) Rice bran oil was the sole diet that improved milk yield with an increase in protein content. However, adding rice bran oil to the diet of grazing dairy ewes had only minor effects on altering milk and cheese PUFA composition. Together with flaxseed oil, rice bran oil significantly enhanced consumer acceptability of ripened cheese; 5) Canola oil was found to have minor but statistically significant effect on milk yield, body condition score, and docosapentaenoic acid (DPA, 22:5n-3) content in milk; 6) Sire breed and its interaction with diet mainly affected milk production, but not milk quality, in which crossbred Awassi x East Friesian had higher milk yield than pure-bred Awassi. Taken together, these outcomes suggest that oil supplements and crossbreeding can be utilised by Australian sheep milk producers in pasture-based systems to improve production traits and cheese eating quality to increase farm-gate value.