The use of a promising global gene pool, which is expressed in the importation of animals of different genetic breeding, creates certain problems of adaptation to different natural and climatic conditions
(Kuznetsov et al., 2011). The study of adaptation features of cattle in the conditions of intensive technology of exploitation is a very relevant problem today (
Kushnir and Vystavnoy, 2008).
An analysis of the index of adaptation of Holstein cows by intensive technology of exploitation at an industrial complex for milk production in the ecological zone of the northern steppe of Ukraine, depending on their age in lactation, showed (Table 1) that this indicator is less than neutral, is zero, so it is negative. At the same time, if in the cows of the second- fifth lactations the adaptation index was practically equal and averaged -5.5, -5.4, -5.7 and -5.7, then in animals of the sixth lactation it was higher an average of 24.7 (P<0.05), 26.0 (P<0.05) and 21.9%, respectively.
The lowest indicator of adaptation index was characterized by cows at the seventh lactation, which averaged 64.6 units, which was inferior to the animals of the sixth lactation by 36.9% (P<0.05). The low adaptation index was observed in the first lactation cows, which averaged 17.1 units and had high variability, which indicated a rather different reaction to the same conditions of the industrial complex.
Scientists indicate that the size of cows and accordingly, their live weight, has a major impact on feed consumption, which determines the level of dairy productivity
(Kennedy et al., 2003). Animals of different ages and the corresponding indicator of adaptation index were characterized by quite good indices of live weight, which indicated satisfactory conditions of feeding and exploitation, which, however, did not fully satisfy the needs of the organism.
In animals of the first lactation, the live weight averaged 593.4 kg in the second, it increased by 7.2% (P<0.001) to 639.2 kg and in the third by 4.1% (P<0.001) to the level of 672.2 kg. After the third lactation, probably due to some exhaustion and a negative value of the adaptation index, the live weight of cows in the fourth lactation decreased by 8.6% (P<0.001) relative to the indicator of the third lactation and averaged 618.9 kg. In the sixth and seventh lactations, the live weight of the cows stabilized at an average of 578.0-578.4 kg.
The analysis of the duration of the productive period in cows of the first to the seventh lactation showed that it exceeds the norm (305 days) by 1.33-1.50 times, that is, exceeds 400 days, which is obviously indicative of low reproductive ability and long, respectively, service period and period between calving.
Researchers
(Kolver et al., 2007) indicate that lactation in dairy cows can be continued beyond the standard (305 days) due to low efficacy artificial insemination, leading to an extended interval between calving. Several researchers have suggested that the causes of prolonged lactation may lie in the negative interrelation between milk secretion and cow fertility
(Friggens et al., 2010).
However, a prolonged lactation period provided a high overall level of milk productivity. Thus, in the first, second and third lactation period from animals was received, on average 10056.8, 10339.8 and 10495.6 kg of milk, which in terms of 4% was respectively 9789.7, 10068.7 and 10264.0 kg. In the fourth to fifth lactation, dairy production relative to the third lactation increased by 3.4% (P<0.001) and 3.3%.
During the sixth to seventh lactations, the level of milk productivity of animals reached the maximum value and averaged 11682.6 and 11124.3 kg of physical milk or 1155.3 and 10952.0 kg, respectively, of 4% milk.
The level of productivity of cows in terms of 305 days of lactation shows their genetic potential and to the greatest extent can characterize its realization with age that is in the context of lactations. In the first lactation cows were characterized by a relatively low level of milk yield, since it averaged 7868.1 kg of physical or 7648.4 kg of 4% milk, in the second lactation - increased by 9.6% (P<0.001) to 8705.8 kg of physical or 8479.8 kg of 4% milk, in the third lactation - increased by 2.4% (P<0.001) to 8919.5 kg of physical or 8729.0 kg of 4% milk.
After that, the adjusted level of cow productivity in the fourth lactation increased again by an average of 2.7% (P<0.01) and amounted to 9165.2 kg of physical or 8992.8 kg of 4% milk. Already at the fifth, sixth and seventh lactations, the level of animal productivity stabilized at 8956.6-9065.8 kg of physical or 8815.2-8909.6 kg of 4% milk.
Over the last four decades, milk production per cow has increased dramatically in North America and Europe thanks to successful breeding programs, as well as improved feeding and containment systems
(Bauman et al., 2006).
Scientists indicate that milk composition depends on the feeding methods and genetic characteristics of the cows (
Roca-Fernández et al., 2012), as well as seasonal changes throughout the year
(Heck et al., 2009).
Analysis of the qualitative composition of cow’s milk at different lactations showed that the mass fraction of fat was high enough and at the first and second lactations were at the level of 3.82 and 3.83%, respectively. In the subsequent, in the third - seventh lactation, this figure did not fall below, although it did not rise above the indicator of 3.89%, which was higher than the values of the first and second lactations in absolute terms, respectively by 0.07 and 0.06%.
The mass fraction of protein in cows’ milk was substantially inferior to fat and averaged by seven lactations averaging 3.23-3.28%. The ratio of fat to protein in milk of lactating cows remained at the normal level, which ranged from 1.17-1.20.
According to the indices of milk yield and mass fraction of fat and protein in milk, their products were obtained from animals, the amount of which increased dynamically from the first to the seventh lactations. The dynamics of cow’s milk protein production over seven lactations practically repeated the curve of milk fat production. Considering the total production of milk fat and protein from cows in different lactations, it should be noted that it also increased from the first to the sixth lactation and in the seventh only decreased slightly.
According to the size of the milk yield and live weight, the animals had different indicators of milk yield. In the second and third lactation, the indicator of the milk coefficient of animals was, on average, 1580.5 and 1564.1 kg. In the fourth lactation of cows, this ratio was higher by 9.4% (P<0.001) and 10.4% (P<0.001), respectively.
Significantly higher milk yields were in cows in the fifth lactation, which was at the level of 1863.2 kg and exceeded the value of animals in the fourth lactation by 6.3% (P<0.01). Animals in the seventh and sixth lactations had high milk yields, respectively, in 1921.9 and 2021.9 kg, which was higher than the fifth lactation cows by 3.1 and 7.8% (P<0.05). At the same time, the milk coefficient in animals of the first lactation was high enough, but the error of the mean indicated a large discrepancy in this indicator.
The intensity of exploitation of cows in different lactations shows that in the third to sixth lactations their coefficient does not exceed 23 kg of milk per day of period between calving and ranges from 23.2 to 23.9 kg. At the same time, this indicator in animals of the second lactation averaged 22.9 kg of milk, which is less than the value of cows in the third lactation by 2.4% (P<0.001). The highest rate of cow intensity exploitation was in the seventh lactation, where it averaged 24.2 kg, which was 5.2% more than animals in the second lactation (P<0.05). The lowest intensity of exploitation was in the first-heifers, where this figure did not exceed 21.0 kg.
For dairy cows, reproductive function will be high if effective artificial insemination occurs within the first three to four months after calving (De Vries, 2006). This is consistent with the negative genetic correlation between milk production and cow health
(Ingvartsen et al., 2003) and by production and reproduction (
Berry D.P.et_al2003), although this negative association is not universal
(Bello et al., 2012).
A significant excess of normal lactation duration in Holstein cows indicated that a certain amount of loss of calves. Thus, animals in the second and third lactations received, on average, 0.32 head of calves and in the seventh - 0.33 heads. In the fourth to fifth lactations, these losses were slightly higher, averaging 0.34 heads. The highest loss of calves were in cows in the sixth lactation and averaged 0.51 heads, which was higher than the rate of cows of the fourth to fifth lactations by 33.3% (P<0.01) and the value of animals of the second and third lactations - by 37.3% (P<0.01). Large of loss of calves from a prolonged lactation period were observed in cows in the first lactation.
Delayed reproduction improves lactation resistance because the development of pregnancy has a negative effect on milk yield, especially in the last trimester of lactation
(Brotherstone et al., 2004). Infertility, which is a consequence of high metabolism, is a predicted physiological response of the organism, not a pathological condition
(Knight et al., 1999).
Heredity determines and conditions of life make the development of the organism. However, in animals with approximately the same heredity under the influence of different environmental conditions (feeding, care and maintenance, features of operation), the formation of traits is not equally
(Lopez et al., 2015).
The large variability of such averages, such as adaptation index, milk yield and loss of calves at first-heifers, indicated that these indicators were not even. To clarify this issue, all first-heifers livestock have been formed into four groups, depending on the level of productivity.
At the first level of productivity (>12000 kg of milk, n=412), the index of adaptation of first-calf heifers averaged -16.6±0.27, at the second (8100-12000 kg, n=1442) -11.4±0.19, at the third (5100-8000 kg, n=2677) -3.4±0.014 and at the fourth (5000 kg, n=79) -5.5±1.59 units.
Scientists conclude that early identification of cows that are sensitive enough to adaptation problems allows the use of certain herd management strategies
(Steeneveld et al., 2013). Today, there is a wealth of knowledge about the early diagnosis of diseased cows
(Trevisi et al., 2012), but very little is known about the identification of animals with good ability to adapt to new lactation in specific ecological and natural conditions.
