Spirulina: Dual-purpose lamb supplement - Breed and sex effects on productivity and product quality

This thesis tested the effect of Spirulina supplementation and its interactions with sire breed, sex and nutritional plane on Australian dual-purpose lamb productivity and product quality. It was hypothesised that Spirulina supplementation would interact with sex, sire breed and plane of nutrition to affect wool and meat quality traits, haematological metabolites, body conformation, liveweight and feed intake indices of lamb productivity. Secondary objectives of assessing the independent effects of sire breed, sex and plane of nutrition on the fatty acid composition of lamb were also investigated. A total of 48 lambs randomly allocated to treatment groups balanced by sire breed (Black Suffolk, Dorset, Merino, and White Suffolk), sex (ewes and wethers) and Spirulina supplementation levels (CONTROL – 0mL, LOW – 50mL, MEDIUM – 100mL, and HIGH – 200mL) was used. These lambs were allocated into two feeding trials with basal diets of differing planes of nutrition – low and high planes of nutrition which represented simulated-drought and pasture-fed diets respectively. In both trials, lambs were fed daily with 150 g barley grain and assigned Spirulina supplementation level as a 1:10 w/v water suspension using a drenching gun prior to being released for grazing on ryegrass pastures. Each feeding trial lasted for 9-weeks including a 3-week adjustment phase. Data collected throughout the feeding trial included; weekly body conformation and liveweight measurements and feed intake; midside wool and blood samples; carcass samples and dressed weight; and feed composition. Wool and meat quality traits, haematological metabolites, body conformation, liveweight and feed intake indices of productivity were analysed in SAS with Spirulina supplementation level, sire breed, sex, plane of nutrition and their second-order interactions used as fixed effects. It was evident that Spirulina supplementation level, sire breed, sex and nutritional plane significantly affected productivity and product quality in Australian dual-purpose lambs, in that; 1) Medium and high Spirulina supplementation levels improved liveweight and growth during drought periods of low nutritional planes; 2) Spirulina supplementation affected physical wool quality traits only when interacting with sire breed; 3) As Spirulina supplementation level increased, so did gamma-glutamyl plasma concentrations and significant interactions of supplementation level with sex had an impact on glucose, Aspartate aminotransferase, and magnesium. Interactions of level of supplementation with sire breed influenced creatinine, gamma-glutamyl and albumin/globulin ratios; 4) Spirulina had no effect on intramuscular fat levels but reduced fat levels when the lambs were on a high nutritional plane; 5) High levels of Spirulina supplementation were associated with increase in subcutaneous fat melting point; and 6) Spirulina level did not reduce feed intake and had no detrimental effect on wool quality of lambs. Furthermore, regardless of Spirulina supplementation level, sex, sire breed and nutritional plane influenced fatty acid profile as an indicator of meat quality. Consequently, the hypothesis was accepted. As an outcome of this thesis, Australian dual-purpose lamb operations can apply Spirulina supplementation to best optimise product quality and productivity. It permits informed decisions when tailoring animal management systems and responding to dietary shifts. The impacts of sire breed, sex and plane of nutrition on lamb product quality and productivity contributes to the existing knowledge of supplementing ruminants with microalgae. This thesis demonstrates that Spirulina is a beneficial and useful protein-rich supplement for Australian dual-purpose lamb operations