This dissertation investigates: (1) the implications of including high-yielding energy sorghum under the Renewable Fuels Standard (RFS2) program; (2) the effects of RFS2 with and without projected climate change scenarios on U.S. agriculture; (3) the spatial distribution of cattle breeders in Texas to quantify how climate factors influence cattle breed selection. In the RFS2 energy sorghum work, the ability of the agriculture sector to meet the fuel requirements of RFS2 is examined with and without energy sorghum being a possibility using an agricultural sector model. The results show that energy sorghum would be a valuable contributor that would be used as a feedstock producing over 13 billion gallons per year of cellulosic ethanol. Without the presence of energy sorghum it is found that switchgrass serves as the major cellulosic ethanol feedstock. Findings also indicate that the presence of high-yielding energy sorghum does relax commodity prices and export reductions except for grain sorghum as energy sorghum competes with grain sorghum production. In addition, the results show that the introduction of energy sorghum has minimal effects on GHG mitigation potential in the agricultural sector. In the RFS2 and climate change research, the analysis shows that climate change eases the burden of meeting the RFS2 mandates increasing consumer welfare while decreasing producer welfare. The results also show that climate change encourages a more diversified use of biofuel feedstocks for cellulosic ethanol production, in particular crop residues. In the cattle breed research, summer heat stress is found to be a significant factor for breed selection: positive for Bos indicus and negative for Bos taurus and composite breeds. The estimation results also indicate a price-driven trade-off between Bos taurus and Bos indicus breeds.

Milk production has been evaluated not only by genetic potential but there are also a lot of indicators. The potential milk production of the herd depends on the correct link between the genetic potential and the system of selection, feeding and nutrition, reproduction and the breeding environment and health of animals. The aim of the thesis was to produce a literary overview of milk production, milk composition and influences that can influence the composition of milk. For the selected herd to evaluate the effects on the monitored indicators of the milk composition and to statistically evaluate them. For discarded dairy cows to determine the age and reason of culling and lifelong milk production.

The objectives of this research were firstly, to investigate if dairy cattle genotypes in NZ exhibit genetic variation in environmental sensitivity and to determine if this genetic variation is statistically significant from a genetic evaluation perspective, and secondly, to use genetic information including environmental sensitivity data to simulate dairy cattle responses to changes in nutritional regime and variation in climate. A comprehensive review identified that simulation models either overlook, or do not represent environmental sensitivity information where genotypes and breeds respond differently when exposed to variations in environment. A large dataset of daily and total lactation records (yields of milk, fat and protein) from herds participating in the progeny testing of sires from 1989 to 2002 was obtained to test for differences in the environmental sensitivity of dairy cattle in New Zealand. Production data was matched with environmental data relating to climate, herd size, altitude and herd average production levels (a proxy for feeding level). The statistical analyses applying univariate and bivariate multibreed models to environmental character states identified minimal sire re-ranking between environmental character states as measured by genetic and rank correlations. However, differences in yields of milk, fat and protein between New Zealand Jersey and overseas Holstein Friesian systematically diverged with production level, in herds expected to use different levels of supplements. These results suggest New Zealand Jersey cattle are best suited to a grassland-type environment, and overseas Holstein Friesian cattle are more suited to an intensive-type environment. A phenotypic analysis identified thermal environment (cold and hot conditions) significantly affected the expression of production traits in Holstein Friesian, New Zealand Jersey and Holstein Friesian x New Zealand Jersey cattle. Holstein Friesian dairy cattle were more susceptible to the effects of heat conditions than New Zealand Jersey cattle with yields of milk, and concentrations of fat and protein of the former compromised at a lower value for temperature humidity index. Dairy cattle performance is likely to be compromised by heat more frequently than cold conditions in New Zealand. A simulation model that considers how dairy cow genotypes respond to different environments, incorporating the results presented above, was then developed. An initial estimate of feed intake is used to define cow genetic potential based on estimated breeding values for total yields milk, fat and protein, and environmental sensitivity information. A mammary gland module then predicts daily yields of milk, fat and protein based on the cow's genetic potential after considering her age, stage of lactation, body condition score, nutritional status and thermal environment. Live weight change is also predicted via a body energy stores module, which considers the effect of age, stage of lactation, current body condition score, nutritional status, and an estimated breeding value for body condition score. Feed intake is predicted from the requirements for maintenance, growth and pregnancy, and the genetic drive for yields of milk, fat and protein and body fat change. The predictive ability of the model was tested using information from a prior study with two Holstein Friesian genotypes managed in a pasture-based system. The model simulated to a high degree of accuracy, mean values for yields of milk, fat and protein, and concentrations of fat and protein of each genotype. Various tests identified the major source of error between simulated and observed values were due to a lack of simulated variation. In conclusion, the extent of genetic variation in environmental sensitivity for total lactation yields of milk, fat and protein within the range of New Zealand environments are not sufficient to warrant the formation of separate breeding schemes for distinct environments. However, New Zealand Jersey cattle are best suited to a grassland-type environment, and overseas Holstein Friesian cattle are more suited to an intensive-type environment. Genetic variation in the suitability of different breeds for specific environments existed within breeds. A simulation model was developed that was able to simulate the effect of genotype, environment and genotypic differences in environmental sensitivity on daily cow performance.

The study was carried out at the Laboratory of Animal Breeding Value Establishment and Selection of Lithuanian Veterinary Academy in the time of postgraduate studies from 2003 to 2005. During the last seven years Lithuanian red and red-and-white controlled dairy cattle breeds average yield increased 41.7%, milk fat production - 50.9%, milk proteins production – 46.1%. Between milk fat and milk proteins was found medium positive correlation coefficient (rp =0.36-0.56; p<0.01), which show milk fat increasing has positive effect to milk proteins increasing. Correlation coefficient between milk production and milk fat, milk proteins is very high (rp =0.87-0.96; p<0.01). The analysis of Variance showed the breed influence on reproductive traits of cow to be statistically reliable (p<0.001). The breed had the greatest influence on cows age during calving. The influence of bulls line on many traits of cows exterior is statistically reliable (p<0,001).