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    Dietary crude protein and nitrogen utilisation in two contrasting dairy systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand
    (Massey University, 2020) Correa-Luna, Martin
    This thesis evaluated the efficiency of crude protein utilisation (ECPU) in dairy cows and nitrogen (N) utilisation efficiency (NUE) of two pasture-based dairy systems differing in intensification levels in New Zealand. During two consecutive seasons, in the low-intensity production system (LIPS), 257 cows were milked once-daily with low supplementation, and in the high-intensity production system (HIPS), 210 cows were milked twice-daily with higher supplementation. At every herd test, ECPU was calculated as protein yield (PY) divided by crude protein intake (CPI), estimated from feed intake. Milk urea (MU) was measured in early-, mid-, and late-lactation. Urinary N was estimated by back-calculation from estimated faecal N, taking into consideration N contained in milk and in body tissues. Pasture allocation represented 93% and 65% of the total intake for LIPS and HIPS cows, respectively, resulting in higher CPI for LIPS cows throughout the lactation. Compared to HIPS cows, LIPS cows produced 22% and 16% less milk and protein, with 32% higher MU, and 25% lower ECPU. Urine N was 34% higher in LIPS cows but faecal N was 5% higher for HIPS cows. A multivariate predictive model of ECPU was developed, including milk production performance, live weight variation, diet composition and quality along with climatic variables. The model accurately predicted the ECPU in an internal validation dataset (RPE = 6.96%, R2 = 0.95). Milk urea was not selected as a predictive variable of ECPU, considering that cows of higher ECPU also had higher MU. Compared with cows of high MU genetic merit, cows of lower MU genetic merit had lower milk production and similar ECPU. A whole-farm assessment of NUE, N losses and financial analysis was undertaken. On whole-farm level, LIPS produced 23% less milk and NUE was 31% lower when compared to HIPS. The lower MY along with the 35% higher N fertiliser applied on LIPS produced a higher N surplus per ha causing higher N losses when compared to HIPS. Despite the higher feed costs of HIPS, profitability was 16% higher because of milking more cows with higher MY when compared to LIPS.
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    The protein requirement of juvenile silver trevally (Pseudocaranx georgianus) to optimise growth in hatchery environments : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Manawatu, New Zealand
    (Massey University, 2017) Elvy, Jordan
    Aquaculture is a growing primary industry in New Zealand. Currently the industry is comprised of three main species: GreenshellTM mussels, Pacific oyster, and King Salmon. The introduction of a white fleshed fish presents obvious commercial opportunity and production gains for New Zealand aquaculture. Silver trevally provides this opportunity and has the potential to further develop the industry. When developing a new species for aquaculture an understanding of their nutritional requirements at the different life stages is required. This thesis investigates the protein requirement of juvenile silver trevally. Silver trevally (67.5±12.0g) were randomly assigned to 12 tanks, 15 fish per tank. Four isoenergetic diets ranging in crude protein (CP) content from 30 to 60% CP were fed, in triplicates, for 12 weeks. Growth, including specific growth rate (SGR), did not significantly differ between diets. Feed efficiency was lowest in fish fed the 40% CP diet compared with the other three diets. Protein retention was highest in fish fed the lowest protein diet. Condition indices in silver trevally were unaffected by the protein content of the diet. Overall, this experiment was inconclusive on the ideal protein level in the diet. A palatability trial was carried out to determine if feed intake varied among diets. For comparison a commercial pellet from Ridley’s (50% CP) and a gel diet (20.4% CP) used by Plant & Food Research was also included in this trial. Twenty-four fish from the growth trial were allocated to two tanks for the palatability trial. Four behavioural responses were observed: the food item was ignored; fish approached the food but did not ingest; the fish took the food into their mouths before spitting it out; and the food was ingested. The 60% CP experimental diet, a commercial pellet, and a gel diet had significantly higher rates of intake than the other diets, with the 30% CP diet having the lowest rate of complete ingestion. The 60% CP and gel diet had the lowest rate of food being ignored. The most palatable diets were the 60% CP diet and the gel diet.
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    The nutritional value of proteins with special reference to A) The availability of amino acids in meat meals to chicks, and B) The chemical changes with heat-damage of pure proteins : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biochemistry at Massey University
    (Massey University, 1974) Wilson, Margaret Nellie
    Meat meals are highly variable in protein quality and this may be due in part to heat-damage. This possibility was investigated by estimating the available lysine content of meat meals by chick growth assay. In addition, the combined urinary and faecal excretion of dietary amino acids by chicks, fed a meat meal as the sole source of protein, was determined, and by subtraction from the amount consumed, values for the apparent retention of dietary amino acids were obtained. In a second part of the study, the mechanism of heat-damage to pure proteins was investigated. Since cross-linkages may form during heat-damage of proteins, enzymatic digests were examined for the presence of peptides with enzyme-resistant linkages. Samples of unheated and heat-damaged haemoglobin or globin were digested with either trypsin, or exhaustively, using several proteolytic enzymes. Chick growth assay for lysine. A chick growth assay for lysine was developed using wheat gluten as the protein source in a semi-purified diet. The meat meals were added to the basal diet either at the expense of starch or by isonitrogenous substitution of wheat gluten. Estimated potencies based on weight gain varied with the method of meat meal addition to the basal diet. This variation was probably due to an effect on the appetite of the chicks as estimates based on food conversion efficiency did not differ significantly with the method of meat meal inclusion. The percentage of lysine biologically available in eight meat meals ranged from 61 to 105%, suggesting that some meals had been heat-damaged. Apparent retention of dietary amino acids. Estimates of the apparent retention of essential amino acids in six meat meals ranged from 79 to 100%. The apparent retention of lysine was generally much higher than the estimated potencies by chick growth assay. The difference in the two biological estimates indicated that other factors, apart from digestibility, and absorption and urinary excretion of peptides and amino acids, must be responsible for the reduced availability of lysine in heat-damaged proteins. Tryptic digests of unheated and heated haemoglobin and globin. Several large fragments were isolated from digests of heated globin which were not present in digests of unhealed globin. The fragments had more than one amino-terminal but individual peptides could not be separated. It was not possible to determine if cross-linkages were present. Exhaustive enzyme digests of unheated and heated globin. A peptide was isolated from digests of heated globin which was not present in unheated globin digests. Results obtained indicated that the peptide was a cyclic tetrapeptide composed of equal quantities of lysine and aspartic acid. It was suggested that the peptide was the result of cross-linkages formed during heat-damage of globin, between the β-carboxyl groups of aspartic acid and the E-amino groups of lysine. It is considered that the formation of covalent bonds with the E-amino groups would account for an appreciable proportion of the decreased availability of lysine in heat-damaged proteins.
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    Aspects of dietary protein quality for the growing pig : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University
    (Massey University, 1984) Moughan, Paul James
    A study of several aspects of dietary protein quality for the growing pig is described. The study was conducted in three parts. Reservations regarding the interpretation of three recent empirical estimates of the ideal amino acid balance for the growing pig prompted the first part of the study. A diet (basal diet) was formulated in which enzymatically hydrolysed casein supplemented with synthetic amino acids formed the sole protein source. The balance of essential amino acids in the diet approximated the mean of the three published estimates. Eight entire male pigs (boars) of 28 Kg initial liveweight, confined in metabolism crates, were fed the basal diet for 20 days and thereafter a protein-free diet for a further eight days. Mean daily excretion of urinary urea nitrogen over six-day collection periods was 93 mg/Kg0.75 for pigs fed the basal diet and the corresponding value for the protein-free diet was 19 mg/Kg0.75. Assuming that the difference between these values was attributable to deamination of amino acids from the basal diet, this corresponds to an efficiency of utilisation of dietary protein of 0.940. It was concluded that the amino acid pattern of the basal diet approximated an ideal balance. Part two of the study entailed the determination and evaluation of estimates of the apparent ileal digestibility of crude protein and amino acids for the growing pig and included a comparison of protein digestibility in the rat and pig. Samples of ileal digesta were collected from boars prepared with T-piece cannulae in the terminal ileum. Values for the digestibility of crude protein and amino acids in barley-meal, pea-meal, meat-and-bone-meal, fish-meal and a mixture of enzymatically hydrolysed casein and synthetic amino acids are cited. In an evaluation of the determined digestibility values ten boars received a barley-, pea-, meat-and-bone-, fish-meal diet and ten a control diet containing enzymatically hydrolysed casein and synthetic amino acids as its sole protein source. The gross amino acid composition of the latter diet equalled the determined apparent ileal digestible amino acid composition of the barley-based diet. Accepting that the control protein source was completely digestible and that the two feeding regimes were iso-caloric, the similar growth characteristics of pigs on the two diets suggested that apparent ileal amino acid digestibility coefficients are accurate measures of the degree of amino acid digestion and absorption in the growing pig. Preliminary results showed close agreement between the rat and pig for the apparent ileal digestibility of crude protein in barley-, meat-and-bone- and fish-meal. In the third part of the study a deterministic computer model which simulates the digestion and metabolism of dietary nitrogen in the growing pig was constructed. The model was based on the concept of a partitioning of daily dietary nitrogen intake in pig growth. Initial validation exercises demonstrated that results obtained from simulation were in close agreement with observations from experimentation with the live animal.