Effect of protein and energy intake on digestion and nitrogen metabolism in wethers and on ovulation in ewes

Abstract

Two experiments were conducted to investigate the basis for an increase in ovulation rate in ewes given improved nutrition prior to mating.Sixteen wether sheep were used in the first experiment in order to screen physiological and nutritional variables likely to be affected by protein and energy intake. They were given low protein (LP) and high protein (HP) diets (19-1 and 35-2 g nitrogen per kg dry matter (DM)) each at four levels of energy intake (range 7-67 to 27-06 MJ gross energy per day). Effects of treatment on digestibility and partition of digestion between the rumen and intestines were small but increased nitrogen intake increased both nitrogen retention and the concentration of some essential amino acids (EAA) in plasma. The dietary treatments imposed on the wethers had been given to 800 ewes previously in a separate trial designed to predict ovulatory response to dietary and energy intakes. When the variables measured in the wether sheep were compared with predicted ovulation for ewes given the same treatments, the strongest relationship was with plasma concentrations of branched-chain amino acids (BCAA; r = 0-95; P < 0-001). Correlations with other EAA were weaker (r = 0-61; P < 001) and were not significantly related to concentrations of non-essential amino acids (NEAA) in plasma (r = -0-21).Eighty ewes in experiment 2 were given an LP diet, blood samples were taken and ovulation rate determined by laparoscopy. One group of 20 ewes was maintained on the diet and another group of 20 was given an HP diet starting on day 7 of the oestrous cycle. Blood samples were taken 5 days later and numbers of ova determined during the next cycle. There were no changes in the number of ova present in ewes maintained on the LP diet, but a change to the HP diet increased ovulation rate from 1-47 to 1-89 eggs per ewe. Ewes which had single or multiple ova when given the LP diet (pre-treatment) had similar concentrations of amino acids in their blood, but those given the HP diet increased blood concentrations of BCAA by proportionately 0-58 and other EAA by 0-29 whilst NEAA were unaffected. Ewes which increased their ovulation rate when given the HP diet had a greater increase in blood BCAA concentration than those which did not increase their ovulation rate. Both the concentration in blood and the magnitude of increase in BCAA concentration appear to affect the number of eggs released. This concept is supported by evidence that BCAA are able to exert regulatory effects on mammalian protein metabolism under some circumstances.

Effect of different dietary crude protein levels on performance, N digestibility and some blood parameters in Kivircik lambs

“…Despite some researchers suggested that there was a correlation between plasma urea level and dietary protein level in sheep (Lindberg and Jacobbsson, 1990;Waghorn et al, 1990), Kronfeld et al (1982) suggested the opposite. Despite some researchers suggested that there was a correlation between plasma urea level and dietary protein level in sheep (Lindberg and Jacobbsson, 1990;Waghorn et al, 1990), Kronfeld et al (1982) suggested the opposite.…”

Performance and metabolic pattern of feedlot lambs using soyabean hulls associated to different non-protein nitrogen sources

“…Outro fator que influencia a concentração de ureia no sangue é a quantidade de proteína ou de nitrogênio na dieta (Roseler et al, 1993;Hoffman et al, 2001) ou, mais concretamente, a quantidade de compostos nitrogenados absorvidos no trato gastrointestinal (Payne & Payne, 1987). Existe, assim, relação direta entre a ingestão de proteína ou de nitrogênio aparentemente digestível e a concentração de ureia plasmática (Lindberg & Jacobsson, 1990;Waghorn et al, 1990).…”

“…Há, portanto, maior desperdício de nitrogênio na forma de amônia quando fornecidas dietas com ureia convencional. Essa hipótese contraria relatos de Wittwer et al (1993) de que os níveis de ureia também podem ser influenciados pela relação energia/proteína da dieta. A avaliação dos níveis de Tabela 3 -Demonstração numérica e percentual da classificação das carcaças (nível de acabamento) para cordeiros confinados utilizando diferentes níveis e fontes de nitrogênio não-proteico β-hidroxibutirato poderia ter contribuído para a conclusão desta hipótese, uma vez que níveis elevados de β-hidroxibutirato indicariam baixo aporte energético da dieta (Gonzales et al, 2000).…”

A mixture of the branched chain amino acids leucine, isoleucine and valine increases ovulation rate in ewes when infused during the late luteal phase of the oestrous cycle: an effect that may be mediated by insulin

“…From these observations it is unlikely that increased concentrations of these BCAAs are respon¬ sible for the increase in ovulation rate following lupin supplementation. Nevertheless, positive relationships between the blood concentrations of the BCAAs, ovu¬ lation rate and nutritional state (Waghorn et al 1990) do suggest that the levels of BCAAs in the diet are significant factors associated with ovulation rate responses to nutrition.…”