Effects of induced hypothyroidism on weight gains, lactation, and reproductive performance of primiparous Brahman cows.

Thrift, Todd; Bernal, Andrés López; Lewis, Andy; Neuendorff, D. A.; Willard, C C; Randel, R.D.

doi:10.2527/1999.7771844x

Cited by 28 publications

(26 citation statements)

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“…Os resultados deste experimento são diferentes das observações de Moraes et al (1996) e de Thrift et al (1999b), que induziram ao hipotireoidismo vacas Brahman e observaram maior ganho de peso, melhor condição corporal e melhor eficiência alimentar. De acordo com Bernal et al (1999), a razão mais provável da melhora da performance em animais hipotireóideos é usar menos energia para a manutenção e outras atividades, por exemplo, absorção de nutrientes.…”

Section: Ptu-propyltiouracilunclassified

“…O hipotireoidismo é caracterizado por diminuir a taxa de consumo de oxigênio por unidade de área corpórea e a maior conseqüência dessas mudanças é o declíneo da taxa de metabolismo basal (Thrift et al, 1999b). Se vacas hipotireóideas têm uma menor velocidade de metabolismo e sua atividade física é reduzida, a proporção da energia da dieta disponível para o crescimento e engorda é aumentada (Trenkle, 1978).…”

Section: Ptu-propyltiouracilunclassified

“…Quanto à performance reprodutiva, avaliando o número de corpos lúteos, a normalidade do ciclo estral e dos estros, não houve diferença entre os controle e os hipotireóideos, o que está de acordo com as observações de Thrift et al (1999a), trabalhando com novilhas Brahman, Thrift et al (1999b), ao estudarem vacas Brahman e Hernandez et al (2003), trabalhando com ovelhas.…”

Section: Differents Letters In the Same Row Differ (P<005)unclassified

“…Resultados semelhantes foram encontrados por Thrift et al (1999a), Thrift et al (1999b) e Moraes et al (1998), ao trabalharem com vacas Brahman alimentadas com feno "hay grass" e concentrado.…”

Section: Treatment Groupunclassified

“…Segundo O'Callaghan et al (1993), a tireóide parece ter influência específica na regulação da transição da estação reprodutiva para o anestro, devido ao papel da glândula associada aos padrões de secreção do GnRH e no feedback negativo do estradiol, permitindo a diminuição na secreção do GnRH estacional. Estudos com vacas Brahman têm evidenciado influência da tireóide sobre a atividade reprodutiva durante o inverno (Randel, 1990), sobre o ganho de peso e sobre a lactação (Thrift et al, 1999b). No entanto não há estudos que expliquem o mecanismo de ação da tireóide e o status energético metabólico sobre a resposta ovariana às gonadotrofinas folículos estimulantes em vacas submetidas ao hipotireoidismo.…”

Section: Introductionunclassified

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Efeito do hipotireoidismo induzido sobre a resposta superovulatória e a digestibilidade aparente da dieta em vacas de corte

Bettini

Moraes²,

Rigolon³

et al. 2006

Acta Sci. Anim. Sci.

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RESUMO.O experimento objetivou determinar o efeito do hipotireoidismo induzido sobre a resposta ovariana ao hormônio folículo estimulante exógeno, a normalidade do ciclo estral de vacas e a digestibilidade aparente. Utilizaram-se 10 vacas Nelore tratadas com propylthiouracil (PTU). A digestibilidade aparente da Matéria Seca, os números médios de corpos lúteos, de embriões, de estrururas colhidas, de estruturas infertilizadas, de estruturas degeneradas, de mórulas, de índice de colheita e de índice de fertilização não variaram significativamente (P>0,05). Os valores médios de T 3 foram de 1,35+0,1 e 1,91+0,1 ng mL -1 , de T 4 de 20,95+1,37 e 61,82+1,37, de TSH 7,95+0,36 e 2,61+0,36, respectivamente, para os animais tratados e controle, havendo diferença significativa (P<0,05). Desse modo, pode-se concluir que não houve efeito de hipotireoidismo induzido sobre a digestibilidade aparente, a produção de embriões, a estereidogênese e a atividade ovariana.Palavras-chave: digestibilidade, embrião, ganho de peso, hipotireoidismo, vacas.ABSTRACT. Induced hypothyroidism effect on superovulatory response and diet apparent digestibility in beef cows. The experiment aimed to establish the effect of hypothyroidism induced on the ovarian response to the exogenous follicle stimulating hormone, the normality of the cows estrous cycle, and apparent diet digestibility. 10 Nelore cows were used and treated with propylthiouracil (PTU). DM apparent digestibility, average numbers of corpus luteum, collected embryos, unfertilized structures, degenerated structures, morulas, collecting rate, fertilization rate, did not present significant variation (P>0.05). In the treated animals, de average T 3 , T 4 , and TSH values were 1.35 ±0.1, 20.95±1.37 and 7.95±0.36, respectively, and in the controls 1.91+0.1 for T 3 , 61.82+1.37 for T 4 and 2.61+0.36 TSH, with significant difference (P<0.05). Based on the results, it is possible to conclude that hypothyroidism did not affect diet apparent digestibility, embryos production, steroidogenesis or ovarian activity.

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Section: Ptu-propyltiouracilunclassified

Section: Differents Letters In the Same Row Differ (P<005)unclassified

Section: Treatment Groupunclassified

Section: Introductionunclassified

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Efeito do hipotireoidismo induzido sobre a resposta superovulatória e a digestibilidade aparente da dieta em vacas de corte

Bettini

Moraes²,

Rigolon³

et al. 2006

Acta Sci. Anim. Sci.

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Plasma concentrations of thyroxine in dairy cows exposed to 60 Hz electric and magnetic fields

Burchard

Nguyen

Rodríguez

2006

Bioelectromagnetics

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Two experiments were carried out to assess the effects of electric and magnetic fields (EMF) on blood thyroxine (T4) in dairy cattle. In experiment 1, 16 lactating pregnant Holstein cows were exposed to 10 kV/m, 30 microTesla (microT) EMF. The animals were divided into two groups of eight animals each. Each group was exposed to EMF according to one of two treatment sequences of three periods of 28 days each. Sequence 1 was EMF OFF-ON-OFF and sequence 2 was EMF ON-OFF-ON. During the last day of each treatment period, blood samples were collected every 4 h for 24 h to estimate T4 plasma concentrations. In experiment 2, 16 nonlactating, nonpregnant, multiparous Holsteins were exposed to 10 kV/m, 30 microT EMF. The animals were divided into two groups of eight animals each. Each group was exposed to EMF according to one of the two treatment sequences described above, except that each period amounted to the number of days corresponding to one estrous cycle. During treatment, blood samples were collected every other day for T4 analysis. In both experiments, the light cycle emulated a short photoperiod (8 h light/16 h dark). During the ON periods, the animals were exposed to EMF for 16 h, 8 h of the light period plus the first 8 h of during the dark period. In experiment 1, exposed animals did not have any change in T4 plasma concentrations due to treatment (P = .0968), but, the time of sample collection revealed a significant difference (P = .0012). In experiment 2, the effect of period (P = .0009) and the treatment by days interaction (P = .0003) were statistically significant. We conclude that a worst case scenario exposure of dairy cattle to 10 kV/m, 30 microT EMF influences, in a moderate fashion, the blood levels of thyroxine.

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Influence of Exogenous Triiodothyronine (T3) on Fecal Shedding of Escherichia coli O157 in Cattle

et al. 2007

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Fecal prevalence of Escherichia coli O157 in ruminants is highest in the summer months and decreases to low or undetectable levels in the winter. We hypothesize that the seasonal variation of this pathogen is a result of physiological responses within the host animal to changing day length. The thyroid is an endocrine gland known to respond to changing day length. Two experiments were conducted to determine if a hyperthyroid status would initiate fecal shedding of E. coli O157 in cattle during the winter when shedding is virtually nonexistent (winter experiment) or influence cattle actively shedding E. coli O157 (summer experiment). Yearling cattle were group-penned under dry-lot conditions, adjusted to a high concentrate ration, and randomly assigned to treatment: control (1 mL corn oil injected s.c. daily) or triiodothyronine (T(3); 1.5 mg suspended in corn oil injected s.c daily). Cattle were individually processed daily for collection of fecal and blood samples. Treatment with exogenous T(3) produced a significant change in serum thyroid hormone concentrations indicative of a hyperthyroid status in both experiments. No differences (P>0.10) were observed in fecal shedding of E. coli O157 in the winter experiment. In the summer experiment, fecal shedding of E. coli O157 was decreased (P=0.05) by administration of T(3) during the treatment period (days 1-10), tended to be lower (P=0.08) during the following 7-day period of no treatment, and was lower (P=0.01) when examined across the entire experimental period. Results of this research indicate that the thyroid or its hormones may be involved in the seasonal shedding patterns of E. coli O157 in cattle.

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Effects of induced hypothyroidism on weight gains, lactation, and reproductive performance of primiparous Brahman cows.

Cited by 28 publications

References 20 publications

Efeito do hipotireoidismo induzido sobre a resposta superovulatória e a digestibilidade aparente da dieta em vacas de corte

Efeito do hipotireoidismo induzido sobre a resposta superovulatória e a digestibilidade aparente da dieta em vacas de corte

Plasma concentrations of thyroxine in dairy cows exposed to 60 Hz electric and magnetic fields

Influence of Exogenous Triiodothyronine (T3) on Fecal Shedding of Escherichia coli O157 in Cattle

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