Altering milk composition through genetic selection

Detailed mineral profile of milk, whey, and cheese from cows, buffaloes, goats, ewes, and dromedary camels, and efficiency of recovery of minerals in their cheese

Milk and dairy products are important in the human diet not only for the macronutrients, such as proteins and fats, that they provide, but also for the supply of essential micronutrients, such as minerals. Minerals are present in milk in soluble form in the aqueous phase and in colloidal form associated with the macronutrients of the milk. These 2 forms affect the nutritional functions of the minerals and their contribution to the technological properties of milk during cheese making. The aim of the present work was to study and compare the detailed mineral profiles of dairy foods (milk, whey, and cheese) obtained from cows, buffaloes, goats, ewes and dromedary camels, and to analyze the recovery in the curd of the individual minerals according to a model cheese-making procedure applied to the milk of these 5 dairy species. The detailed mineral profile of the milk samples was obtained by inductively coupled plasma-optical emission spectroscopy. We divided the 21 minerals identified in the 3 different matrices into essential macro- and microminerals, and environmental microminerals, and calculated the recovery of the individual minerals in the cheeses. The complete mineral profiles and the recoveries in the cheeses were then analyzed using a linear mixed model with Species, Food, and their interaction included as fixed effects, and Sample within Species as a random effect. The mineral profiles of each food matrix were then analyzed separately with a general linear model in which only the fixed effect of Species was included. The results showed that the species could be divided into 2 groups: those producing a more diluted milk characterized by a higher content of soluble minerals (in particular, K), and those with a more concentrated milk with a higher colloidal mineral content in the skim of the milk (such as Ca and P). The recoveries of the minerals in the curd were in line with the initial content in the milk, and also highlighted the fact that the influence of the brine was not limited to the Na content but to its whole mineral makeup. These results provide valuable information for the evaluation of the nutritional and technological properties of milk, and for the uses made of the byproducts of cheese making from the milk of different species.

Options for genetic improvement of milk composition

Genetic improvement is constrained by the long-term and cumulate nature of genetic improvement, by the economic rewards for making genetic change and by the variances and covariances among traits of interest. Genetic change is cumulate, so that small annual changes make substantial differences over time. This cumulate nature of genetic improvement dictates the importance of identifying long-term goals driven by robust economic signals and then adhering to them. The economic rewards for genetic improvement will ultimately determine the uptake and therefore the success of any breeding program. In developed countries the value of milk can be divided between the weight of water, fat and protein produced. Water generally has a negative value due the cost of handling, removal and disposal. Fat and protein have varying values depending on the market, but both will always have underlying positive values. Genetic variances and covariances among the aggregate composition traits, water, fat and protein, are such that simultaneous increase in the yield of all three is considerably easier than improvement of just one, or improvement of one while decreasing others. Selection for simultaneous increase of fat and protein percentage will also be successful, but at the price of not increasing fat and protein yield nearly as rapidly as when selecting directly on yield traits. In virtually all developed countries, the optimum selection goal will be for some combination of increased fat and protein yield that may lead to a gradual increase in the protein to fat ratio. Genetic polymorphisms in several protein genes have been associated with yield and with milk processing properties, but are unlikely to play more than a minor role in overall selection. There is some evidence of genetic variation in milk fat composition, but the level of variation and economic incentives for change mean that selection for milk fat composition is not worthwhile. Thus, with the exception of very slow changes in the water to fat to protein yield ratio, genetic improvement does not seem a particularly suitable route for altering milk composition.

Effect of breed, protein genetic variants and feeding on cows' milk coagulation properties

One hundred and thirty-seven (Holstein (41), Montbéliarde (42) and Tarentaise (54)) dairy cows in first or second lactation received during winter one of two levels (high, H; low, L) of energy intake, and were later fed identically at pasture. Thrice in winter and twice at pasture, the chemical composition and coagulation properties of individual milks were measured. Milk from Holstein cows had lower casein and calcium contents, and poorer coagulation properties (curd firming time and curd firmness) than that from Montbéliardes and Tarentaises (P< 0·01). These differences practically disappeared when taking into account the distribution of the differentκ-casein variants and milk casein content.κ-BB milks had coagulation properties 20–50% superior, according to characteristic, to those of AA milks. In the three breeds, animals from the H group had casein contents higher by 1·4 g/l than those of the L group, which induced a significant improvement in curd firming time, curd firmness and cheese yield. Turning out to pasture induced an increase of 0·02 in milk pH, and improved milk coagulation properties. These changes did not appear to result entirely from the parallel increase in milk casein content.

Determining the Amount of Rumen-Protected Methionine Supplement That Corresponds to the Optimal Levels of Methionine in Metabolizable Protein for Maximizing Milk Protein Production and Profit on Dairy Farms

The profitability of feeding rumen-protected Met (RPMet) sources to produce milk protein was estimated using a 2-step procedure: First, the effect of Met in metabolizable protein (MP) on milk protein production was estimated by using a quadratic Box-Cox functional form. Then, using these estimation results, the amounts of RPMet supplement that corresponded to the optimal levels of Met in MP for maximizing milk protein production and profit on dairy farms were determined. The data used in this study were modified from data used to determine the optimal level of Met in MP for lactating cows in the Nutrient Requirements of Dairy Cattle (NRC, 2001). The data used in this study differ from that in the NRC (2001) data in 2 ways. First, because dairy feed generally contains 1.80 to 1.90% Met in MP, this study adjusts the reference production value (RPV) from 2.06 to 1.80 or 1.90%. Consequently, the milk protein production response is also modified to an RPV of 1.80 or 1.90% Met in MP. Second, because this study is especially interested in how much additional Met, beyond the 1.80 or 1.90% already contained in the basal diet, is required to maximize farm profits, the data used are limited to concentrations of Met in MP above 1.80 or 1.90%. This allowed us to calculate any additional cost to farmers based solely on the price of an RPMet supplement and eliminated the need to estimate the dollar value of each gram of Met already contained in the basal diet. Results indicated that the optimal level of Met in MP for maximizing milk protein production was 2.40 and 2.42%, where the RPV was 1.80 and 1.90%, respectively. These optimal levels were almost identical to the recommended level of Met in MP of 2.40% in the NRC (2001). The amounts of RPMet required to increase the percentage of Met in MP from each RPV to 2.40 and 2.42% were 21.6 and 18.5 g/d, respectively. On the other hand, the optimal levels of Met in MP for maximizing profit were 2.32 and 2.34%, respectively. The amounts of RPMet required to increase the percentage of Met in MP from each RPV to 2.32 and 2.34% were 18.7 and 15.6 g/d, respectively. In each case, the additional daily profit per cow was estimated to be $0.38 and $0.29. These additional profit estimates were $0.02 higher than the additional profit estimates for maximizing milk protein production.

Effects of selection and crossbreeding strategies on industry profit in the New Zealand dairy industry

The effects of selection and crossbreeding on the New Zealand dairy industry net income were evaluated with a deterministic model over a 25 yr planning horizon. Several mating strategies involving Holstein-Friesian, Jersey and Ayrshire cattle were evaluated. These strategies were straight breeding, upgrading to Holstein-Friesian, upgrading to Jersey, upgrading to Ayrshire, use of the best bulls irrespective of breed and two- and three-breed rotational crossbreeding. Industry productions of milk, fat, protein, and lactose were calculated assuming that 12,000 kg of dry matter per hectare was utilized from 1,224,911 hectares of pasture. Profitability was the difference between income (international sale of whole milk powder, casein, butter, and beef from salvage animals) and costs (farm expenses, milk collection, manufacture, and marketing). Casein and whole milk powder were valued at NZ$8.345 and NZ$3.306/ per kilogram, respectively, over 25 yr. Butter was valued at NZ$2.995/kilogram for base year production levels and NZ$0.45/kilogram for marginal increases in production. Upgrading to Holstein-Friesian resulted in the highest industry net income (NZ$1119 million) followed by straight breeding (NZ$1086 million) and two-breed rotational Holstein-Friesian x Jersey (NZ$1076 million). However, if the marginal value of extra butter production was assumed equal to the average base value, then upgrading to Jersey resulted in the highest industry net income (NZ$1185 million) followed by two-breed rotational Holstein-Friesian x Jersey (NZ$1177 million) and use of the best bulls (NZ$1173 million). Future costs and prices of dairy products have major impact on mating strategies.

Toward altering milk composition by genetic manipulation: current status and challenges

The implementation of large-scale genome mapping and sequencing has improved the understanding of animal genetics. A large number of gene sequences are now available to serve as regulatory elements or genes of interest. Although the central thrust of this work is focused on understanding disease states, the manipulation of normal metabolic processes is feasible. To date, the genetic manipulation of livestock has been limited to the permanent addition of genes of clinical interest. This study explores the utility of genetically engineered cattle as a means of altering milk composition to improve the functional properties of milk, increasing marketability. Improvements would include increasing the concentration of valuable components in milk (e.g., casein), removing undesirable components (e.g., lactose), or altering composition to resemble that of human milk as a means of improving human neonatal nutrition. The protracted time lines of genetically modifying dairy cattle has prompted the development of animal models. A model for dwarf goats is discussed in terms of circumventing the lengthy time lines involved in generating transgenic cattle and allowing for an accelerated expansion of research in molecular genetics of dairy animals. Thus, the genetic manipulation of dairy cattle is feasible and could have significant impacts on milk quality, attributes of novel dairy products, and human health.

Optimizing the herd calving pattern with linear programming and dynamic probabilistic simulation

Until recently, little attention has been paid to the influence of seasonal variation in performance and prices on the optimal calving pattern of a herd. A method was developed to determine the herd calving pattern that is farm-specific and optimal with use of linear programming. The required technical and economic parameters are calculated with a dynamic probabilistic simulation model of the dairy herd. The approach was illustrated with a situation in which the objective was to maximize the gross margin of the herd and the annual milk production of the herd was restricted, resulting in an optimal calving pattern: all heifers calved during August. When, in addition, only home-reared replacement heifers were allowed to enter the herd, heifer calvings took place from July to October. The gross margin was reduced by only Dfl. .13/100 kg of milk ($1 US = 1.80 Dfl.) as a result of the additional constraint. The sensitivity of the optimal calving pattern of herd was determined for lower reproductive performance and when seasonal price variation was ignored. The method described herein is a flexible tool for determining the optimal calving pattern of herd, taking into account farm-specific inputs and constraints.

Nutrient requirements and feed costs associated with genetic improvement in production of milk components

Dietary requirements for NEL and absorbed true protein were summarized for marginal production of milk components because of genetic improvement through selection. Shelled corn and soybean meal were used to meet marginal nutrient requirements and were assigned variable concentrations of absorbed true protein, depending on rumen-available energy and protein. Mean ratios among national averages for shelled corn to milk prices and soybean meal to milk prices (DM: standardized milk, dollars per kilogram) over a recent 25-yr period were .52 and 1.20, respectively. Stability of these relationships over time permits estimation of feed costs from milk price as prices inflate. Feed costs per kilogram of component, expressed as kilograms of standardized milk with equivalent value, were 1.00 for lactose, 1.89 for fat, and 3.49 for protein. Costs of milk protein were higher if production of absorbed true protein was limited by rumen-available energy, suggesting that selection for fat or lactose, in addition to protein, may be beneficial. High feed costs for milk protein indicate a need for adequate compensation to producers for milk protein and consideration of feed costs during selection. A net value index is proposed that considers feed costs associated with marginal production of individual milk components.

Optimal genetic improvement for the high producing herd

Genetic merit for milk production is increasing over 150 kg of milk/yr in the Holstein cow population. Nationwide decreases in payments for fat differential since 1987 have not been counter-balanced by similar increases in payments for protein differential, resulting in a steady increase in the value of carrier. Protein yield should be emphasized rather than specific casein or whey fractions of protein because national recording, evaluation, and payment structures are not in place. Genetic merit of bulls for markers may differ across families, making selection for marker traits of limited value in current breeding schemes. Conformation traits that appear to have the highest correlation with measures of herd life are udder depth, for udder attachment, and teat placement. Selection for health traits is difficult because of limited genetic information. National evaluations for SCC are being developed, but average difference between extreme bulls is only slightly more than one linear SCC. Managers of high producing herds should continue with primary selection emphasis on production traits. The greatest challenge to dairy producers is to develop management systems, particularly in nutrition, that allow maximal expression of genetic potential.

Metabolizable energy and absorbed protein requirements for milk component production

Metabolic pathways of milk component synthesis were used to estimate metabolizable energy and absorbed protein requirements for lactation. Amounts of ATP and AA used for synthesis of each component from absorbed substrates were determined. Coefficients were adjusted to account for additional inefficiencies and to define requirements in terms of dietary supply based on NRC energy requirements and N balance data. Assuming that 10% of glucose required was derived from AA, metabolizable energy and absorbed protein requirements were 6.02 Mcal and .136 kg/kg of lactose, 13.43 Mcal and .127 kg/kg of fat, and 7.57 Mcal and 1.069 kg/kg of protein, respectively; an additional .144 Mcal/kg of milk was required for milk volume. For production of milk containing 4.8% lactose, 3.5% fat, and 3.3% protein, absorbed protein required for lactose and fat may account for 14.1 and 9.6%, respectively, of total absorbed protein required for milk production. Efficiency of protein utilization for milk protein synthesis may be as high as 90% when 10% of glucose requirements must be supplied by AA. Expressing nutrient requirements for lactation on a component basis enables calculation of requirements for milk production of any composition and does not rely on correlations between major milk components.

Crossfostering and early development of natural killer cytotoxic activity in various inbred mouse strains

In the present study using crossfostering among three inbred mouse strains (C57BL/6, DBA/2, and Balb/c) we compared the effects of lactation with milk of different compositions on the development of NK cells cytotoxic activity. The results show that the pups from C57BL/6 and DBA/2 mice exhibit a significant early increase of NK cells cytotoxic activity when fostered by Balb/c dams, in comparison to those fostered by natural mothers. The analysis of proteins, lactose, and lipids showed difference among the strains for all components. Strain effects for days of lactation were also observed. The naso-anal length and the body weight of young mice showed differences with the strain of fostering mothers. The results indicate that the characteristic of maternal milk composition interacts with the inbred genetic susceptibility of the pups to elicit the full expression of the level of NK activity.

Lactation curve estimation for use in economic optimization models in the dairy industry

Monthly data on completed lactations were employed to estimate a three-stage least squares lactation curve model for milk production, milk fat content, milk protein content, and body weight change in lactating Holstein cattle. In comparison with previous work on the lactation curve, our study employed an augmented incomplete gamma model of the lactation curve, a simultaneous rather than single equation estimation technique, monthly rather than daily or weekly observations, and a pragmatic treatment of the genetic background of individual cows using sire proof data. In addition to considering genetic and dietary effects on the lactation curve, the model isolates the seasonal effect of calving date and current production month as well as the age of the cow. By allowing for the simultaneous explanation of various measures of cow performance, the model accommodates formulation of diets tailored for individual cows or groups of cows and can be used in profit-maximizing mathematical programming models. Diet, production, and body weight changes are determined simultaneously and are not independent of one another.

The potential for genetic change in milk fat composition

Effecting genetic improvement requires genetic variation, a mechanism of selection, and an economic incentive for the improvement. Limited data suggest that there is within-breed genetic variation in milk fat composition, but accurate estimates are lacking. There is some evidence for modest differences among breeds. Substantial differences exist among species, indicating that substantial genetic change in fat composition is biologically possible. The economic incentives for genetic change are not clear. Changes in fat composition that would improve the quality of one milk product would often be detrimental to other products. Such changes would best work where subpopulations produced milk for specific end products. Such division of the industry would be difficult to organize and might impede existing improvement programs. Changes in fat composition that increased consumer acceptance of milk products, such as reduced saturated fat concentration, might increase the market for milk products. However, only large changes in composition are likely to affect consumer acceptance; thus, the gradual changes of conventional genetic improvement would produce little or no return to the breeder. Genetic changes that reduced processing costs or increased product value might have low to moderate economic value, inducing slow rates of change. Production of transgenic animals might provide a route for genetic alteration of fat composition in the future. Such improvement would most likely be cost effective in a subdivided production industry in which milk from cows of a particular genotype can be directed to a particular milk product. It is concluded that although alteration of fat composition could be achieved, it is unlikely to be an important component of genetic improvement of dairy cattle.

Selection strategies and artificial evolution

Artificial selection results in biolgical changes, creating artificial evolution. When using selection indexes, the artificial evolution depends on the relative economic (or other) weight of traits in the breeding objective, and on the phenotypic and genetic variances and covariances among these traits and the traits recorded in the selection index. As shown here, the selection strategy (in this case, individual selection versus progeny test selection) can also have marked effects on the kind of artificial evolution produced. Thus, where economic weights are uncertain, choice between alternative selection strategies might take into account the different types of animal or plant resulting.