A host of nutrients are needed by cattle to support functions associated with life, and to grow, reproduce, and nourish their offspring (i.e., produce milk). A vast amount of resources have been expended to quantify the amounts of specific nutrients needed to perform these function so that economically efficient diets can be formulated. Feeding diets that provide adequate, but not excessive, amounts of nutrients helps improve profitability of dairy operations while reducing the environmental impact of dairy farms. The trace minerals zinc, copper, manganese, and selenium are components of a wide variety of enzymes and proteins that support metabolism, growth, production, and reproduction. Trace mineral supplements are added to dairy cattle rations to prevent mineral deficiencies, and supplementation has traditionally been provided in the form of inorganic salts.

The aim of this study was to compare crown-rump length (CRL), trunk diameter and number of heartbeats of embryos and fetuses in heifers and pluriparous cows and also to compare the growth pattern of these structures and their correlation with fetal age. Six nulliparous heifers and seven pluriparous cows (third to seventh of gestation) of the Holstein breed were selected and impregnated. Ultrasonographic measurements were performed twice weekly during days 26-80 of their pregnancies. By day 80, there was no significant difference in CRL and trunk diameter of embryos and fetuses of heifers and pluriparous cows. All of the measurements had a highly significant correlation with fetal age (P<0.0001) except for pluriparous cows in which the fetal heartbeat was significant at p<0.05. The correlation coefficients (CC) of the CRL, trunk diameter and number of heartbeats in the fetuses of heifers and cows were as follows: 0.97, 0.98, -0.74 and 0.97, 0.98, -0.23, respectively. The growth pattern of the CRL and trunk diameter was quadratic in heifers and cows. Also the heartbeat in the fetuses of heifers decreased progressively in a quadratic pattern from day 31 through day 80. However, heartbeat in the fetuses of cows changed in an approximately stable or intermittent range. Moreover, standard error of heartbeats in the fetuses of cows was high. It was concluded that all of the measurements in heifers and cows are suitable for estimation of fetal age, except for heartbeat in the fetuses of pluriparous cows. This measurement is not practically recommended, due to a low CC and high standard error. In addition, there was no significant difference between the CRL and trunk diameter in heifers and cows until day 80 and this difference probably will become more pronounced in late pregnancy

This study aimed to estimate the effect of environmental factors on variation of the longevity and the ge-netic parameters of the trait in Holstein dairy cows in Iran. The records of 181738 cows in the years 2001 to 2018 were provided by the Animal Breeding Center of Iran (Karaj, Iran). Profitability in dairy herds de-pends on animal survival in the herd, which is provided by reducing involuntary culling and increasing the voluntary culling in the herd. The survival was defined as the lifespan, the lifetime milk, fat, and protein yield after first calving, and lifetime days in milk. The effect of environmental factors on traits and risk of culling was estimated using Survival kit and cmprsk statistical packages. The variance components were estimated by Gibbs sampling method based on exponential distribution, incomplete data, and survival analysis. The effects of herd, season, and age of calving on traits were significant (P<0. 001). The risk of culling of cows with difficult calving was higher than others. The risk of culling of cows calved in spring was higher than in other seasons. The heritability of different traits of survival estimated to be 0. 0067-0. 0147. The results showed that the effect of different environmental factors on variation of longevity is significant, and the heritability of the trait is low. However, a review of the literature indicates that, despite the low heritability of the trait, it can be improved in a population through genetic selection. This approach is justified, as longevity is not only important for the farmer from the economic point of view, but it also affects the increase of animal welfare and social acceptance of the dairy sector.

Free radicals are normally produced by living organism, at controlled production rate they perform physio-logical functions as signal transduction molecules. However, situations leading to an overproduction that surpasses antioxidant capacity creates oxidative stress. Consequently, damage to the cell membrane, pro-tein, DNA and cell death are observed. Dairy cattle are susceptible to oxidative stress. Situations such as infections, metabolic disorders and heat stress are known to cause oxidative stress in cattle by depleting body antioxidants concentrations or by increasing endogenous free radical production. The organism re-sponse to oxidative stress by activating cell factors that after evaluating the damage to cell, a repair or death signal will be programmed. The objective of this review is to empower the reader with knowledge related to oxidative stress and to provide information on the situations leading to this type of stress and the cellular response to it in dairy cattle.

Introduction Determining the production function is one of the most effective ways to monitor the continuity of milk production, as it indicates the relationship between the intake of feedstuff and milk production. To explain the production function in breeding programs and estimate regression coefficients, third-degree nonlinear regression is used. The milk production curve follows a third-degree rule, and therefore, it can be divided into three basic parts. Second-degree production functions cannot accurately represent a milk production curve from the beginning of lactation to the time of dryness, because they only depict the second-degree performance of milk production from the beginning of lactation to the peak of lactation. The aim of this research was to investigate the effects of the production function in breeding programs and their potential use in selecting superior animals.Materials and Methods In order to recognize the opportunities for profitability in a herd, we first need to create the right production function. To achieve these goals, data on milk production and feed intake from one of the industrial farms in Tehran province were used. Various methods were examined in this study: 1- using OLS approach in R environment to estimate the milk production function, 2- using the Peykani extended ordinary least square (POLS) method, 3- estimating the breeding value of milk production using POLS function and physical milk production (field data) using Wombat software, 4- comparing OLS production functions obtained in R with the POLS production function, 5- Conducting genetic evaluation of animals and ranking dairy cows. When the production functions were obtained according to the POLS program, the optimal amounts of feed consumption and milk production were calculated. The breeding value of milk production was estimated using a repeatability model with permanent environmental effects that consider covariance between records of an animal and this was done using the Wombat program. Finally, cows were ranked based on their genetic rank.Results and Discussion The estimated functions based on the ordinary least squares method were incorrect in terms of signs and coefficients, and did not fit the milk production curve well. Based on the findings of this study, the non-linear regression model POLS is the best in the curve fitting and economical production of milk. The results show that with milk yield corrected using the optimal feed intake by the POLS model the ranking of the animals has changed and the breeding value of the animals is more accurately estimated. By using the breeding values estimated in this method, one can select the best animals as the parents of future generations.Conclusion The ability to estimate the production function based on the POLS method, which is used to create a standard curve of dairy cows is very high. Our results contribute significantly to the field of animal breeding by shedding light on the role of production functions in enhancing breeding programs and facilitating the identification of high-performing animals. The insights gained from our study could drive improvements in animal selection processes and ultimately enhance milk production efficiency.