4. Production traits in twin- and single-calving cows before calving

In another study [30], the rate of occurrence of multiple pregnancies was found to increase noticeably (p ≤ 0.01) as the milk production level of the cows increased. Higher yielding cows are predisposed to double ovulations, which directly affects the incidence of twinning [39]. High energy diets offered in the early lactation are a contributing factor in the rate of double ovulations [23, 24]. For breeders, it is worth noting that the rate of twin births increased significantly (p ≤ 0.01) from 0.43% in heifers between 2000 and 2003 to 0.77% in heifers between 2010 and 2012. This is thought to be linked to increased production levels of the active population, because the yield of cows in their first lactation in 2000 was 5969 kg compared to 8215 kg for cows in their first lactation that calved in 2012.

pregnant by the 13th day of service if the first or second insemination was successful. On analysis of age of first calving, it was demonstrated that on average the age of first calving in pregnant heifers was 27.5 months, and there was also no significant difference between twinning and nontwinning heifers. The lack of deviation is due to the management system and

The calving to service period prior to a viable pregnancy was on average 73.9 days, showing no significant difference between twinning and nontwinning cows. The cows that were

There is a statistically proven difference between twinning and nontwinning cows (p = 0.047) in the length of open period, which was 109.3 days for nontwinning and 104.6 for twin-calving cows, meaning that twin-calving cows required a shorter service period by 4–5 days than

Cows carrying twins had an average gestation length of 274.0 days, which was confirmed to be shorter than their herd mates carrying single calves for 278.7 days. There was a significant (p < 0.001) difference in this study of nearly 5 days due to the type of calving. The average length of gestation was 276.3 days. The significant contributing factors to the total variance were the following: type of calving, calf gender, and calving season, 64.22, 17.32, and 10.92%,

Calving interval of the herd was 398.2 days. A relevant difference was detected between the twin-calving and single-calving cows. The calving interval in twin-calving cows was 392.2 days, shorter than the calving interval in nontwinning cows, which was 404.2 days. A

This farm study assumed that cows that would carry twins have a better body condition, which leads to better fertility provided the housing and feeding all the cattle receive are the same. It was concluded that the beginning of the breeding phase for young animals is dependent on the decision of the farmer and it will be similar for every heifer on that farm. The first part of the investigation was concerned with events only occurring once in life of a heifer. However, later characteristics that occur repeatedly in life of a dairy cow were analyzed, and in all cases, the characteristics were taken into consideration before calving, demonstrating differences between the length of the calving interval, open days, and gestation during the herd's

life. This shorter calving interval can be seen as advantageous in a dairy herd.

4. Production traits in twin- and single-calving cows before calving

In another study [30], the rate of occurrence of multiple pregnancies was found to increase noticeably (p ≤ 0.01) as the milk production level of the cows increased. Higher yielding cows are predisposed to double ovulations, which directly affects the incidence of twinning [39]. High energy diets offered in the early lactation are a contributing factor in the rate of double ovulations [23, 24]. For breeders, it is worth noting that the rate of twin births increased significantly (p ≤ 0.01) from 0.43% in heifers between 2000 and 2003 to 0.77% in heifers

nontwinning cows, due to their better fertility and higher chance for conception.

when the farmer chose to inseminate them.

66 Ruminants - The Husbandry, Economic and Health Aspects

difference of 12 days is significant (p < 0.001).

nontwinning took 73.6 days.

respectively.

Milk yield is positively correlated to frequency of multiple pregnancies [3, 4]. In an analysis of 91,008 calvings between 1974 and 1985, it was shown that twinning was much more frequent in Holstein Friesians compared to the Polish Black-and-White breed.
