Milk production and constituents of beef cows with different breed compositions

Background: There are two classes of factors that affect cow milk production and, as a 15 consequence, the performance of calves: environmental and genetic factors. Considering the 16 importance of milk production of beef cattle, it is essential to measure the milk production of 17 such cows. However, such estimation presents some difficulties, especially when cows are 18 raised exclusively in a grazing regime. This study aimed to evaluate the milk production and 19 the nutritional composition of beef cows from eight different breed compositions (Angus: 20 ANAN, Hereford: HHHH, Nellore: NENE, Hereford-Angus: HHAN, Angus-Hereford: 21 ANHH, Nellore-Angus: NEAN, Angus-Nellore: ANNE, and Caracu-Angus: CRAN) raised 22 under continuous natural pasture grazing, besides evaluating the calves' adjusted weight at 210 23 days until weaning. Results: NEAN cows were the most productive but did not differ from ANNE, ANHH, and 25 CRAN, with estimated average yields of 6.2, 5.97, 5.93 and 5.86 kg/day, respectively, 26 throughout the lactation period. NENE cows presented the lowest yields, with a daily average 27 of 4.61 kg, although this value did not differ significantly from those of HHHH, ANAN and 28 HHAN cows, which had means of 4.67, 4.79 and 4.84 kg/day, respectively. Calves of CRAN, 29 NEAN, and ANNE cows were heavier than calves of ANAN, HHAN, HHHH, and NENE cows 30 at weaning, not differing from ANHH cows, which in turn also had heavier calves than HHHH 31 cows. NEAN, ANNE, HHHH and NENE cows had higher concentrations of total solids in milk 32 than ANAN and ANHH. Conclusions: In conclusion, the crossbreeding of genetically more distant breed beef cows. climate,


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For a more accurate analysis of milk production, data from cows that did not undergo 139 all evaluations and cows with non-standard fat concentrations (< 1 or > 7%) were neglected, 140 resulting in the exclusion of five ANAN, two CRAN, nine HHAN, ten NEAN, five HHHH, 141 three NENE, three ANHH, and three ANNE cows.

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In the analyses concerning milk production, individual lactation curves were initially where: WP= week of peak lactation; PP = milk production at lactation peak (kg); TP210 = total 159 milk production in 210 days of lactation. 160 The persistence of lactation (PER) was defined as the daily linear decrease in milk 161 production between the peak lactation and weaning times [21]: The parameters a and k, as well as the other variables derived from the lactation curve, 176 were considered dependent variables for each cow and were analyzed in a completely 177 randomized design by using the SAS PROC GLM [22].

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Lactation curve and milk production 207 The parameters of the lactation curve (i.e. "a" and "k") were affected (P < 0.05) by the 208 breed composition of the cows in the two methods of evaluation (Table 1). The lactation curve 209 obtained by the MM methodology ( Figure 1) shows a greater difference among the analyzed 210 genotypes, unlike the CWD lactation curve (Figure 2). Although there are no inconsistencies, 211 the differences between breed compositions are not so evident in Figure 2.

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The TP210 estimated by MM was significantly influenced (P < 0.05) by the lactating 213 cow genotype (Table 1) The differences between total yields in different studies reflect the great influence of 234 environmental and genetic conditions to which beef cows are subjected to. This allows us to 235 outline animal management and breeding strategies to maximize the benefit of maternal ability 236 within the breeding system.

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In the genotypes evaluated and, in both situations (i.e. MM and CWD), peak production 238 occurred between the 7th and 11th week of lactation (Table 1). This is consistent with the report 239 by NRC [27] and Rodrigues et al. [15], who found that peak milk production in different genetic 240 groups occurred on average at 8.5 weeks of lactation.

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The breed composition of cows influenced the milk production at the lactation peak (P 242 < 0.05). ANHH and CRAN cows had higher yields than ANAN, HHAN and NENE cows 243 ( to show more expressive decreases in milk production.

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The breed of the bull influenced the total production at 210 days (P < 0.05) only when 260 analyzed by the CWD method (Table 1) using the CWD method, did not find significant differences in the milk production of Hereford 266 cows that nursed Red Angus or Nellore paternal calves.

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The higher milk production of cows suckling crossbred calves may have occurred 268 because of a greater number of feedings per period than pure ones. This is associated with the 269 genetic determination of the calves' temperament and behavior, which, by nursing more 270 frequently, would further stimulate the production of milk by their dams [14,31].

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Corroborating this, Reynolds et al. [32] found that cows with crossbred calves produced more 272 milk (16%) than cows with purebred calves. Therefore, our results suggest that CWD 273 evaluation does not only estimate the cow's milk production capacity but that the behavior of 274 the calf also influences cow milk production because of higher milk consumption. Seemingly, 275 the calves out of Brangus sires had a more active nursing behavior when compared to calves 276 of Braford bulls. 277 We verified an influence of the calving season on total milk production when analyzed 278 by the MM method ( Table 2). Cows that calved at the end of the calving season had low total 279 yields (P < 0.05). In contrast, cows which calved during the first half of the calving period had 280 higher yields at the peak lactation period. This can be justified by the variation in climatic conditions (e.g. temperature, rainfall and, luminosity) between calving periods because climate 282 directly affects the availability and quality of forages [9,33,34]. Therefore, in the present 283 study, cows calving in early spring were favored because this period corresponded to better 284 productivity and quality of regional natural grasses due to a favorable climate [35].

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Regarding the calving order, of the nine categories evaluated by the MM method, the 286 cows 3.1 showed lower milk production at the lactation peak than the majority categories 287 (except 4.18 and 4.2) and lower TP210 than almost all other groups (except 4.18, differing from ANHH cows, which in turn also had heavier calves than HHHH cows. Such 318 results agree with a corresponding higher milk production of cows, confirming that weaning 319 weight is closely related to the cow's milk production [3,47,48]. Several studies have also 320 related weaning weight to maternal milk production regardless of genotypes involved [3,49].

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The correlation between TP210 and CW210 was significant and positive (P < 0.05),    Table 1 Means and standard errors (within parentheses) for lactation curve parameters 'a' and 'k', peak production (PP), week of peak lactation (WP), total production in 210 days of lactation (TP210), persistence (PER), and calf weaning weight adjusted to 210 days (CW210), obtained by mechanical milking (MM) and calf weight difference (CWD) methods, according to breed composition of the cow.   Means within a line and factor with different superscripts differ (P < 0.05).
27 Table 3 Means and standard errors (within parentheses) from lactation curve parameters 'a' and 'k', peak production (PP), week of peak lactation (WP), total production in 210 days of lactation (TP210), persistence (PER), and calf weaning weight adjusted to 210 days (CW210), obtained by mechanical milking (MM) and calf weight difference (CWD) methods, according to the calving order.