|RANDEL, RONALD - Texas Agrilife Research|
|STELZLENI, ALEXANDER - University Of Georgia|
|CALDWELL, LISA - Texas Agrilife Research|
|WELSH JR, THOMAS - Texas Agrilife Research|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2011
Publication Date: 12/1/2011
Citation: Lents, C.A., Randel, R.D., Stelzleni, A.M., Caldwell, L.C., Welsh Jr, T.H. 2011. Function of the corpus luteum in beef heifers is affected by acute submaintenance feeding but is not correlated with residual feed intake. Journal of Animal Science. 89(11):4023-4031.
Interpretive Summary: It is generally well understood that reproduction is controlled by metabolism in animals, but the mechanisms behind this regulation remain poorly understood. During normal production scenarios, beef cattle can experience fluctuations in metabolic state due to changes in their body’s demand for nutrients. Young growing heifers are more sensitive than mature cows to acute changes in intake of nutrients, but the response is variable. This indicates that improvement in the efficiency of beef cattle production can be achieved if the physiological and genetic factors underlying this variability can be identified. To investigate this, scientists determined the residual feed intake, a measure of how efficiently animals utilize feed, of heifers near the time of puberty and measured subsequent function of the ovary in these heifers during acute submaintenance feeding. They discovered that acute changes in nutrient intake impaired normal function of the ovary in a large proportion of heifers. They also found that blood concentrations of insulin-like growth factor-I, a hormone that controls growth of somatic tissue and reproductive function, changed with level of nutrition and was associated with residual feed intake depending when measurements were made. This indicates the relationship between feed efficiency and reproductive performance of cattle likely involves common hormonal pathways and forms the basis for future studies to determine how selection of cattle for residual feed intake affects reproductive performance of replacement beef heifers.
Technical Abstract: Seventy-four Angus and Angus x Hereford heifers were used in two successive years (yr 1, n = 43; yr 2, n = 31) to determine if ovarian function of heifers during acute submaintenance feeding is related to variation in utilization of feed as determined by residual feed intake (RFI). Residual feed intake was determined for heifers beginning at 12.3 ± 0.1 mo of age in yr 1 and at 9.1 ± 0.1 mo of age in yr 2. Heifers were assigned to dry-lot pens (n = 6 to 9 heifers/pen) with electronic gates to measure individual feed intake of a total mixed ration for 70 and 72 d in yr 1 and 2, respectively. Residual feed intake was calculated as the difference between actual DMI and expected DMI from linear regression of DMI on mid-test BW**0.75 and ADG. At 14.4 ± 0.1 mo of age, all heifers were provided a restricted amount of feed to supply 40% of their maintenance energy requirements for 21 d. Estrous cycles of heifers were synchronized with PGF2a on day -10, 0, and 11 relative to start of restriction. Concentrations of progesterone in plasma on d 14 to 21 of restriction were used to determine if heifers ovulated. Overall RFI, ADG and ADFI were 0.00 ± 0.01, 0.83 ± 0.02, and 7.37 ± 0.67 kg/d for yr 1 and 0.00 ± 0.01, 0.50 ± 0.02, and 5.66 ± 0.09 for yr 2. There was no correlation between RFI and BW, ADG, ADFI or ultrasound measure of back fat; nor was RFI related to concentrations of IGF-I in plasma. All heifers lost BW and had reduced back fat (P < 0.001) at the end of restricted feeding. All heifers had reproductive cycles before dietary restriction started. During acute nutritional restriction, 4 heifers became anovulatory. Sixteen heifers had concentrations of progesterone in plasma during restricted feeding that were atypical of normal luteal function. There was no relationship between luteal function during nutrient restriction and RFI of heifers. Circulating IGF-1 was greater at weaning and after restricted feeding in heifers with a lower RFI (> 0.5 SD below the mean) than heifers with a higher RFI (> 0.5 SD above the mean). We conclude that RFI is not related to ovarian function during acute submaintenance feeding but that short-term restriction of nutrient intake can alter ovarian function that may compromise fertility, even in animals that show estrus and ovulate.