EFFECT OF FIRST LACTATION YIELD ON LIFE PERFORMANCE OF COWS

Anna Sawa

ABSTRACT

The studies were carried out on the population of 14215 cows. The first lactation yield, in kg of FCM, significantly differentiated both the yields of subsequent lactations and the indices of life performance of the cows. In high–production herds (with more than 5000 kg FCM), it is justifiable that the requirement should be met for heifer cows to reach the yield that would balance the costs of their rearing (5000–6000 kg of milk), as their high productivity during the first lactation positively influences their life performance, which is important especially from the perspective of the short period of productive life. In other herds, in the case of highly productive heifer cows, the lower the herd production level, the more intensive the following effects should be expected: decrease in the yield of subsequent lactations, lower overall life performance, fertility deterioration, lower number of born calves and shorter productive life.

Key words: productivity of heifer cows, performance traits.

INTRODUCTION

The first lactation is considered as a “training” one, as the organism is still developing. The yield of the first lactation becomes important in the face of the falling trend in the productive life of cows, which has been observed for several years [1, 8, 10, 11, 12]. Juszczak et al. [5], who analysed the problem of the falling trend in the productive life in the scope of rearing cost compensation, stated that German producers aim at increasing even the first lactation yield in order to reach the level that would correspond to the costs, i.e. about 6000 kg of milk. In the herds with high production level, it is justifiable that the requirement should be met for heifer cows to reach the yield that would balance the costs, whereas in the case of the yields that do not exceed 8000 kg of milk, deterioration of reproductive indices and falling trend in life performance should be expected [5]. The results by Gnyp et al. [3] indicate that the yield of heifer cows that exceeded 6000 kg of FCM resulted in significant loss in their further fertility and lower number of calves, and in insignificant decrease of productive life and lower overall production of milk and its components. The studies by Kamieniecki and Stenzel [7], carried out on herds producing about 4000 kg of milk, demonstrated a yield decrease in subsequent lactations of the cows that had exceeded the level of 5000 kg for their first lactation. One should presume that the problem of high first lactation milk yield, in connection with performance traits level (among others lifespan and fertility), will attain more and more importance.

The aim of the present study was to determine the changes in milk yield in successive lactations in relation to the yield level of the first lactation. Bearing in mind that performance traits draw more and more attention, the evaluation of an effect of first lactation yield on life performance of cows was also carried out. The analysis allowed for the fact that the local herd had been improved with the HF breed, and the specificity of management conditions associated with the variability of production levels of the herds was taken into consideration.

MATERIALS AND METHODS

The materials for the study were taken from the SYMLEK system, as well as from the documentation collected by the Regional Animal Breeding Station (OSHZ) in Bydgoszcz. The analysis covered the origin, milk performance, fertility and culling of 14215 cows belonging to the population active in the area of the former provinces: Bydgoszcz, Torun and Włoclawek. The cows included in the study calved for the first time in 1988 (1^st lactation ł 200 days, heifer cows yield ł 2000 kg FCM) and were culled out until the end of 1999. For each cow, the values of the traits that influence life performance were estimated: life FCM yield, lifespan and productive life, number of calvings, number of live–born calves and duration of mean calving interval (CI).

Moreover, in order to evaluate the effect of heifer cows yield on the yield of subsequent lactations (II, III and IV), a group of 3705 cows were selected that completed the fourth lactation and whose lactations were not shorter than 200 days.

In order to characterise the yields in the subsequent lactations and the indices of life performance of the cows, as the effects of first lactation yield x genetic and environmental factors interaction, the analysis of variance was carried out according to the following model:

Ykip = µ + b + lk + gi + p_p + (lp)_kp + (lg)_ki + e kip

µ – overall mean,
b – coefficient of regression on the age on the day of first calving,
lk – effect of k–th FCM level during the first lactation (Ł 4000 kg FCM, 4001–5000, 5001–6000, > 6000), k = 1… 4
gi – effect of i–th genetic group (BW, <50% HF, 50% HF, > 50% HF), i = 1… 4,
p_p – effect pf p–th level of herd yield estimated basing on the average yield of cows in the herd in 1988 (Ł 4000 kg FCM, 4001–5000, > 5000), p = 1… 3,
(lp)_kp – interaction first lactation FCM yield level x herd yield level,
(lg)_ki – interaction first lactation FCM yield level x genetic group,
e kip – random error.

Test F was used to test the significance of the effect of the studied factors on the subsequent lactations yields and life performance traits, and the significance of differences between the means of particular traits within the classification factors was tested with Scheffe test.

RESULTS AND DISCUSSION

The results of the analysis of variance and F test (Table 1) demonstrate that most of the traits are highly significantly influenced by the considered factors and their interactions. It was observed that in the subsequent lactations, the effect of first lactation yield decreased, whereas the effects of herd production level and genotype on FCM yield increased.

Milk production increases with cow's age. The analyses carried out indicate (confirming the results obtained by Kamieniecki et al. [7]) that the rate of yield increase in consecutive lactations is different for the animals of low and high performance (Tables 2 and 3). The cows that attained the 1^st and 2^nd level of FCM yield in the first lactation reached its peak yield in the third or fourth lactation, whereas the high–production heifer cows (group 3 and 4) had their peak yield during the first lactation. The studies by Hibner et al. [4] demonstrated that modern–rearing cows reach their maximum lactation yield in the 3–5^th lactation.

It was observed that the cows that attained higher yield during the first lactation were also characterised by better milk yield in the subsequent lactations. Their predominance, however, varied depending on the herd production (Table 2) and genotype (Table 3). The most intensive increase in milk yield (+49% over the first lactation) was observed for the cows that produced up to 4000 kg FCM as heifer cows, and were kept in the herds of the highest production. Within the first two FCM yield groups of the first lactation, it was observed that the superiority in subsequent lactations increased with the herd production level. The cows whose first lactation yield was 5001–6000 kg FCM, or more than 6000 kg FCM, decreased their yield after subsequent calvings (with one exception). The drop of the subsequent lactation yields of high–production cows was the higher, the lower was the herd production level, which demonstrated improper feeding and care during rearing and the first lactation, and is an evidence that environmental conditions were not adjusted for the needs of high–production animals. Lower increase of yield in subsequent lactations may also result from the fact that the cows achieved their genetic potential already during the first period of production. After subsequent calvings, they remained at the high level of yield, especially in the herds of the highest production (better selection, higher qualifications of maintenance personnel and veterinary service, more rational feeding). Unfortunately, even in those herds, the heifer cows that yielded over 6000 kg FCM did not increase their yield in the subsequent lactations. Other authors draw attention to the influence of management conditions on the yield shaping in subsequent lactations [6, 7]. The studies by Dorynk et al. [2] demonstrate that with the increase of herd breeding level, a decrease in the percentage lactation yield growth rate in relation to the previous lactation was observed.

Analysing the proportional distribution of cows by the first lactation yield groups (Tables 4 and 5), it may be observed that only 32% of the studied population reached the level of 5000–6000 kg FCM as heifer cows; the level deemed as balancing the cost of rearing [9]. The fact should be considered as unsatisfactory. According to Juszczak et al. [5], the cows whose first lactation yield exceeded 5000 kg constituted 60% of the population, however, those studies covered the top herds of the country.

The evaluation of changes in FCM yield for subsequent lactations in relation to the first lactation yield and the genotype led to conclusion that the heifer cows reaching up to 4000 kg FCM had the higher subsequent lactations yields, the higher HF gene share was in their genotype. Maximum yield (by 30–48% higher than in the first lactation) the cows attained at the third lactation, except for the cows of unknown origin. The cows that produced 4001–500 kg FCM as heifer increased their subsequent lactations yield to much lesser extent than their age mates of lower milk yield. The growth of yield in the third lactation, which was the peak for most of the cows, ranged between 9% for BW group and 19% for the F₁ generation. The cows with more than 50% of HF genes increased their yield until the fourth lactation, reaching 24% excess over the first lactation. Among the cows between 5001–6000 kg of FCM first lactation yield, only the group with more than 50% of HF genes increased the yiel d until the third lactation (growth by 6%). The cows that produced more than 6000 kg FCM as heifers the more reduced their subsequent lactations yields, the less HF genes were in their genotype. Dorynek and Kaczmarek [2] observed that BW x HF crossbreds were characterised by higher growth of milk yield in subsequent lactations.

The FCM yields in the first lactations significantly differentiated life performance indices of the cows, and at the same time, the performance shaped differently in the herds of different overall production levels (Table 4). A significant increase in life FCM yield was observed along with the increase of heifer cows’ yield and the overall production of the herd (ranging between 9742 and 21032 kg FCM). Moreover, the cows that were qualified to the group 1 or 2 of first lactation yield demonstrated a trend to have shorter productive life as the overall herd production increased, whereas the tendency was reverse for the other cows. Basing on the present studies, the fertility performance should be considered good for those cows whose yield after the first calving did not exceed 4000 kg FCM (CI about 370 days). The fertility of the cows producing 5001–6000 kg FCM, especially of those with more than 6000 kg of yield, was low (CI 386–494 days). The negative impact of high m ilk productivity on the fertility performance was confirmed by moderate correlation (r = 0.34**, Table 6). For the remaining, lower yield levels, the coefficient of correlation was about 0.12**. The estimated LSM values demonstrate an improvement of fertility performance (represented as CI length) along with the herd production increase (Table 4). The evaluation of reproductive performance, as a number of born calves, demonstrated (like in the studies by Juszczak et al. [5]) its reduction with the increase in first lactation yield, especially if the level of 5000 kg FCM was exceeded, which resulted from the elongation of calving intervals. The cows of the 1^st and 2^nd classes of FCM first lactation yields produced the highest number of calves if they were kept in the herds of middle production level. In the case of the cows of the 3^rd and 4^th classes, the number of calvings grew with the increase in the herd producti on, which would demonstrate very good conditions of maintenance and care in the herds. The analysis allows concluding that the first lactation yield level, optimal from the point of view of the management efficiency, changes depending on the herd production level, which is used as a measure of maintenance conditions quality.

In addition, the first lactation yield x genotype interaction significantly differentiated the life performances of the cows. Among the cows that had not exceeded 4000 kg FCM for the first lactation, the F₁ generation achieved the best life performance (12874 kg FCM, 2034 days of life, 3.42 calves, 366 CI days). Among the remaining cows, regardless their first lactation yield, a trend of increased life FCM yield was observed, longer lifespan and productive life and increased number of calves, along with the advanced improvement with the HF breed. The cows with more than 50% of HF genes, which produced more than 6000 kg FCM for the first lactation, lived the longest (2277 days), produced the most milk (24116 kg FCM) and gave birth to the highest number of calves (3.04).

The relationship between the first lactation FCM yield and life FCM performance was described with the coefficient of correlation, which for the general population of the cows was 0.35** (Table 6). The dependence, considered for the cows divided into first lactation yield groups, indicates that predictions of the cow’s life performance basing on its first lactation are not always precise. Kamieniecki et al. [6] also observed a trend of decrease in the mentioned relationships with the increase in the first lactation yield. Juszczak et al. [5], studying the high–production cow performance indices, concluded that the first lactation yield did not differentiate the life performance of cows, which was 22500–24900 kg FCM.

Another step, important for life performance evaluation, is an analysis of culling factors (Table 7). The cows that achieved the highest first lactation yields were less often sold or culled because of low milk performance, whereas they were more often eliminated due to infertility of casual aCIdents. Gnyp et al. [3] demonstrated that the culling rate caused by infertility or udder disorders increased with the level of the first lactation yields.

CONCLUSIONS

In the evaluation of the first lactation yield, it is advisable to allow for production level of the cow’s herd. In the herds of high production (more than 5000 kg FCM), it is justifiable that the requirement should be met for heifer cows to reach the yield that would balance the costs of their rearing (5000–6000 kg of milk), as their high yield for the first lactation positively influences their life performance, which is important especially from the perspective of cow’s short life span. In other herds, in the case of highly productive heifer cows, the lower the productivity level of the herds, the more intensive following effects should be expected: decrease in the yield of subsequent lactations, lower overall life performance, fertility deterioration, lower number of born calves and shorter life production period.

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