O efeito do estresse térmico associado à produção de leite e índices reprodutivos de vacas da raça Holandesa
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Data
2022-11-07
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Universidade Estadual Paulista (Unesp)
Resumo
O objetivo deste estudo foi avaliar a taxa de concepção de vacas leiteiras sob influencia da produção de leite e estresse térmico ambiental. Um total de 250 fêmeas leiteiras Holandesas foi convertido em 1.238 observações. Essas observações foram de nulíparas que receberam inseminação artificial (IA; n = 297), multíparas com IA (n = 465) e multíparas com inseminação artificial em tempo fixo (IATF; n = 476). As observações foram agrupadas em cinco classes térmicas ambientais, cada uma dividida em variáveis acima ou abaixo do limite de tolerância térmica para as estações climáticas (primavera/verão (Q) vs. outono/inverno (F)); temperatura ambiente (°C, temperatura máxima diurna (TMd) e temperaturas máximas médias (MTM) diárias no intervalo de 50 dias antes do IA/IATF (< 30°C vs 30°C)) e índice de temperatura e umidade ( THI, índice de temperatura-umidade diário (THId) e THI médio diário (MTHI) durante um intervalo de 50 dias antes da IA/IATF, < 72 vs 72); dias em lactação (DEL), produção de leite em litros (L). Houve diferença na taxa de concepção (P/AI) após 30 dias de IA entre nulíparas e multíparas (62,3% [185/297] vs. 24,8% [233/941]) e entre IA e IATF em multíparas (29,9% [139/465] vs. 19,7% [94/476]). A produção de leite foi maior nas multíparas (29,23 0,43 L/dia) do que nas primíparas (25,18 0,28 L/dia). Vacas acima de 201 DEL apresentaram menor produção média de leite (L/dia) em comparação aos intervalos de 1 a 100 DIM e 101 a 200 DIM em primíparas (21,84 0,58 vs. 25,68 0,37 vs. 26,83 0,54) e multíparas (23,84 0,74). vs. 31,85 0,60 vs 30,16 0,74). Houve associação de melhor taxa de concepção em nulíparas quando expostas a menor limiar térmico (estações outono/inverno; ambiente com temperatura < 30°C e THI < 72, quando avaliados em dia e em médias). Em vacas multíparas em lactação a taxa de concepção foi menor quando comparadas a nulíparas e sofreram interferência negativa da produção de leite. O aumento do THId diminuiu a taxa de concepção em nulíparas e multíparas com produção > 32 L/dia. Nas condições climáticas do ambiente tropical, as nulíparas apresentaram melhores taxas de concepção quando comparadas as primíparas e multíparas, mesmo com THId > 72, acreditamos ser resultado da ausência da produção de leite apesar de serem termossensíveis. Por outro lado, vacas primíparas e multíparas em lactação mostraram-se termossensíveis diminuindo a taxa de concepção e probabilidade de prenhez à medida que a produção de leite e THId aumentam para vacas da raça Holandesa criadas em sistema estabulado.
The aim of this study was to evaluate the conception rate of dairy cows under the influence of milk production and environmental thermal stress. A total of 250 Holstein dairy cows were converted in 1238 observations. These observations were from heifers who received artificial insemination (AI; n = 297), multiparous with AI (n = 465) and multiparous with fixed-time artificial insemination (TAI; n = 476). The observations were grouped into five environmental thermal classes, each divided into variables above or below the thermal tolerance threshold for climatic seasons (spring/summer (Q) vs. autumn/winter (F)); ambient temperature (°C) (maximum daytime temperature (TMd) and average maximum temperatures (MTM) daily during a 50 day interval prior to the AI/TAI (< 30°C vs 30°C)) and temperature and humidity index (THI, daily temperature-humidity index -THId, and daily average THI -MTHI, during a 50 day interval prior to AI/TAI, < 72 vs 72); days in milk (DIM), milk production in liters (L). There was a difference in the conception rate after 30 days of AI (P/AI) between nulliparous and multiparous (62.3% [185/297] vs. 24.8% [233/941]) and between AI and TAI in multiparous (29.9% [139/465] vs. 19.7% [94/476]). Milk production was higher in multiparous (29.23 0.43 L/day) than in primiparous (25.18 0.28 L/day). Cows above 201 DIM had a lower average milk production (L/day) compared to intervals 1 to 100 DIM and 101 to 200 DIM in primiparous (21.84 0.58 vs. 25.68 0.37 vs. 26.83 0.54) and multiparous (23.84 0.74 vs. 31.85 0.60 vs 30.16 0.74). There was an association of better conception rate in nulliparous when exposed to lower thermal threshold (autumn/winter seasons; environment with temperature < 30°C and THI < 72, when evaluated in day and in averages). In lactating multiparous cows the conception rate was lower when compared to nulliparous and suffered negative interference of milk production. The increase in THId decreased conception rate in both nulliparous and multiparous with production > 32 L/day. In the tropical environment, nulliparous had better conception rates when compared to primiparous and multiparous, even with THId > 72, which we believe is the result of the absence of milk production despite being thermosensitive. On the other hand, primiparous and lactating multiparous cows were thermosensitive, decreasing the conception rate and pregnancy probability as milk production and THId increase for Holstein cows reared in a stabled system.
The aim of this study was to evaluate the conception rate of dairy cows under the influence of milk production and environmental thermal stress. A total of 250 Holstein dairy cows were converted in 1238 observations. These observations were from heifers who received artificial insemination (AI; n = 297), multiparous with AI (n = 465) and multiparous with fixed-time artificial insemination (TAI; n = 476). The observations were grouped into five environmental thermal classes, each divided into variables above or below the thermal tolerance threshold for climatic seasons (spring/summer (Q) vs. autumn/winter (F)); ambient temperature (°C) (maximum daytime temperature (TMd) and average maximum temperatures (MTM) daily during a 50 day interval prior to the AI/TAI (< 30°C vs 30°C)) and temperature and humidity index (THI, daily temperature-humidity index -THId, and daily average THI -MTHI, during a 50 day interval prior to AI/TAI, < 72 vs 72); days in milk (DIM), milk production in liters (L). There was a difference in the conception rate after 30 days of AI (P/AI) between nulliparous and multiparous (62.3% [185/297] vs. 24.8% [233/941]) and between AI and TAI in multiparous (29.9% [139/465] vs. 19.7% [94/476]). Milk production was higher in multiparous (29.23 0.43 L/day) than in primiparous (25.18 0.28 L/day). Cows above 201 DIM had a lower average milk production (L/day) compared to intervals 1 to 100 DIM and 101 to 200 DIM in primiparous (21.84 0.58 vs. 25.68 0.37 vs. 26.83 0.54) and multiparous (23.84 0.74 vs. 31.85 0.60 vs 30.16 0.74). There was an association of better conception rate in nulliparous when exposed to lower thermal threshold (autumn/winter seasons; environment with temperature < 30°C and THI < 72, when evaluated in day and in averages). In lactating multiparous cows the conception rate was lower when compared to nulliparous and suffered negative interference of milk production. The increase in THId decreased conception rate in both nulliparous and multiparous with production > 32 L/day. In the tropical environment, nulliparous had better conception rates when compared to primiparous and multiparous, even with THId > 72, which we believe is the result of the absence of milk production despite being thermosensitive. On the other hand, primiparous and lactating multiparous cows were thermosensitive, decreasing the conception rate and pregnancy probability as milk production and THId increase for Holstein cows reared in a stabled system.
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Palavras-chave
estresse por calor, lactação, concepção, bovino de leite, heat stress, lactation, conception, dairy cow