عنوان مقاله [English]
Introduction: When the urban population around the capitals or big cities increases, then need an intensive and modern dairy industrial farms or even mega dairy farm to support milk and dairy products demands. Therefore, many family farms shifted to big dairy farms which expecting more specializing and modern technology to be used towards reduction of the cost of milk production per cow. Management of these farms also completely different from housing, reproduction, nutrition and other technical points-of-view. In order to investigate true productive life and milk production during the last 15 years (2006-2020 years), in 20 industrial Holstein mega dairy farms this study was done. All the farms had a specialist in the fields of hygienic condition, calf rearing, balancing the diet, heat and Pregnancy detection and planed mating program for semen selection and breeding to control the production and type performance and preventing the inbreeding which help to use maximum inbreeding coefficient, if required.
Materials and Methods: The correlation between the lengths of true productive life (TPL), maximum lifetime milk production (MLMP305), and maximum lifetime peak of milk production (MLPMP) in 20 industrial Holstein mega dairy farms were investigated. The information recorded in the herd management software in the cattle breeding units, which included the information of the culled cows and all the existed cows in the herds from April 1385 to January 1400, were analyzed. The data includes 176,674 cattle records, of which 43,587 are related to existing cattle and 133,087 data are related to culled ones. The information of the existing cows was done in order to control the information of the herds and also monitor them. Finally, 133,087 data related to existing cows were edited and filled in the computerize program. To calculate the standard milk of 305 days, it is necessary to milk the animals three times a day and the animals have at least 4 monthly records of milk and also that the dryness of these animals has been recorded as the end of the milking period. The Data has been analyzed by univariate method of SAS software (Version 9.4). The Holstein-Friesian cow herds, on average, comprised 2069 cows, with a range from a minimum of 400 to a maximum of 5301 cows. These herds were distributed across 14 provinces throughout Iran. The average age at first calving was 750 days, and the standard 305-day milk yield averaged 12,342 kg during the third lactation. TPL records from 113584 cows and MLMP305 records from 78036 and MLPMP records of 111276 cows were used. The data were analyzed for the correlation between the characteristics of the true productive life, milk production of 305 days and the peak of milk production Also, the linear regression between the true productive life and milk production were analyzed.
Results and Discussion: The average TPL of the animals under investigation is 33.57 months and the standard deviation of the data is 20.77. The average MLMP305 by these animals is 12472 kg and their standard deviation is 2513 kg. The average MLPMP of the animals was 51.83 kg. The highest correlation was between MLMP305 and MLPMP, which is 74.66%. The correlation between TPL and LPMP was 47.88% (P<0.0001) and the correlation between TPL and LMP305 was 33.27 % (P<0.0001). Our results are in accordance with studies such as Van Vleck, 1964, Hudson Van Vleck, 1981, and Ducrocq et al. 1988, but were in contrast with the results of Hare et al. 2006, and Ajili et al. 2007, and Dallago et al. 2022. The highest level of correlation (as expected) is between305-day milk production and the peak of milk production.
Conclusion: The positive correlation between TPL, MLMP305, and MLPMP, shows that the animals with higher peaks also have higher milk production in one lactation period also have a higher true productive life. Considering the high significant positive correlation of this report, by selecting animals with a high production life span, not only can the productive life span be improved in the future generations, but contrary to the existing belief, milk production can also be increased in the future generations. It should be mentioned that the conclusion of this paper is extendable, when we can control all physiological and nutritional factors and have a proper pregnancy detection method which lead to perfect calving management and results that has been done exactly in the farms which we studied.