Browsing by Author "Egan, A.R."
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Item Effect of concentrate supplementation during early lactation on plasma IGF-I concentrations and reproductive performance of dairy cows(2011) Obese, F.Y.; Stirling, T.E.; Stockdale, R.C.; Macmillan, K.L.; Egan, A.R.; Humphrys, S.An experiment was conducted to assess the effects of body condition score (BCS) at calving and level of feed supplementation during early lactation on the Insulin-like growth Factor-I (IGF-I) and reproductive performance in 72 Holstein cows in a pasture-based system following seasonally-synchronized calving. At the start of the seasonal breeding, plasma IGF-I concentrations in cows that had recommenced ovarian activity with detected oestrus were compared with those in anoestrus. The cows (n = 72) were managed over a period of five months to calve in a BCS of 4, 5 or 6 - using a scale from 1 (thin) to 8 (obese). The cows were maintained on pastures and supplemented during early lactation with either 1 or 6 kg grain per day. The BCS at calving did not affect plasma IGF-I concentrations. The plasma IGF-I concentration at week 10 was elevated at the higher level of grain supplementation (87.8 vs. 72.1 ng/mL). Higher conception rate following the first insemination of cows calving with a BCS of 6 (71% vs. 46% and 37% for a BCS of 4 and 5, respectively) was associated with more cows in that group conceiving during the first three weeks of the artificial insemination (AI) programme (75% vs. 46% and 46% for a BCS of 4 and 5, respectively). At weeks 0 and 10, cows that commenced ovarian activity by the start of the intensive AI programme, recorded higher plasma IGF-I concentrations than anoestrous cows. These findings indicate that diet can affect the plasma IGF-I levels, which in turn may be involved in affecting the resumption of cyclic ovarian activity and conception in dairy cows.Item Effect of nutritional status on concentrations of insulin-like growth factor-I in milk from Holstein cows(2011) Obese, F.Y.; Macmillan, K.L.; Egan, A.R.; Stockdale, R.; Humphrys, S.The effect of diet on concentrations of milk insulin-like growth factor-I (IGF-I), and their relationships with plasma IGF-I, and with somatic cell count (SCC) were evaluated in two trials. In Trial1, 32 multi-parous Holstein cows at 4 to 5 wk of lactation received 4 different diets formulated to provide high (H) or low (L) dry matter intake (DMI) with H or L metabolisable energy (ME) density for 5 wk. Dietary treatment did not affect milk IGF-I concentrations, but concentrations were repeatable in individual cows. The intraclass correlation coefficients were 0.78 ± 0.05 and 0.73 ± 0.06 in a.m. and p.m. samples, respectively, when concentrations were measured for 7 consecutive days. The association between milk IGF-I and plasma IGF-I concentration was weaker (R2 = 0.140; P = 0.035) than the association between milk IGF-I concentrations and the natural logarithmic value (Ln) of SCC (R2 = 0.249; P = 0.004). The effects of body condition score (BCS) at calving and level of grain supplementation in early lactation on IGF-I concentrations in milk were evaluated in Trial 2 with 21 Holstein cows that grazed pasture. The BCS at calving did not affect milk IGF-I concentrations; neither did supplementation with 1 or 6 kg of grain. Milk and plasma concentrations of IGF-I were not associated (R2 = 0.002; P = 0.830), whereas the association between milk concentrations of IGF-I and Ln SCC was significant (R2= 0.342; P=0.005). Concentrations of IGF-I in milk were not a sensitive measure of dietary changes in lactating pasture-fed Holstein cows.Item Effects of dry matter intake and metabolisable energy density on the concentrations of insulin-like growth factor-I (IGF-I) and blood metabolites in pasture-fed dairy cows(Ghanaian Journal of Animal Science, 2009) Obese, F.Y.; Rabiee, A.R.; Macmillan, K.L.; Egan, A.R.; Humphry, S.; Anderson, G.A.Blood metabolites including glucose, NEFA, BHB and urea could be used as indicators of nutritional or energy balance in an animal. The plasma concentrations of IGF-1 may also be a sensitive measure of dietary changes. The relationship between IGF-I and the above metabolites in the blood, and their potential in monitoring dietary effects in 32 pasture-fed Holstein-Friesian cows in early lactation were investigated in a 5-wk study. The cows were randomly assigned to four dietary sub-groups and fed one of 4 rations varying in dry matter (DM) and metabolizable energy (ME) concentration (LL: 16.6 kg DM and 174 MJ ME; HL: 17.3 kg DM and 181 MJ ME; LH: 15.4 kg DM and 183.1 MJ ME; HH: 17.9 kg DM and 213.3 MJ ME, with the first letter indicating DM and the second ME). The four rations consisted of pasture, hay and pelleted cereal grain. Plasma IGF-I concentrations were positively associated with glucose (R = 0.587; P<0.01) but negatively associated with BHB (R = - 0.588; P<0.01) and urea (R = -0.372; P<0.05) concentrations at d 35. The relationship between IGF-1 and NEFA concentration was not statistically significant (R = 0.007: P.00.05) at d 35. ME density had grater influence on the proportional changes in blood IGF-1, glucose, BHB and urea concentrations, than changes associated with DM intake. Plasma IGF-I had a higher R2 estimate in its model than any other metabolite at d 14 (R2 = 0.528) and d 35 (R2 = 0.649) of the study, except for BHB at d 35 (R2 = 0.708). The changes in IGF-1 with diet were over a greater range than with the other metabolites, and were indicative of a stronger association of IGF-I with dietary changes.Item Measuring concentrations of insulin-like growth factor-l with an enzyme-linked immunosorbent antibody assay in plasma samples from Holstein cows(Journal of Dairy Science 1(91): 160-168, 2008) Obese, F.Y.; Humphrys, S.; Macmillan, K.L.; Egan, A.R.This study describes the use of a commercial non extraction ELISA to quantify total concentrations of insulin-like growth factor-l (IGF-I) in plasma samples from Holstein cows fed pasture-based diets varying in dry matter and metabolizable energy density. The assays were conducted using the protocols provided by the manufacturer. The ELISA was verified for linearity, accuracy in measuring IGF-I from spiked plasma samples, and precision involving variation within and between assays. Validation also involved comparing results of the ELISA against an established RIA after defatted plasma samples were subjected to acid gel HPLC to dissociate and separate IGF and IGF binding protein complexes. Validation results had low coefficients of variation (CV; intraassay CV of less than 6% and interassay CV of less than 8%) and a high recovery percentage of IGF-I (79%) from samples spiked with unbound IGF-I. The coefficients of determination between the ELISA and the RIA reference assay were 0.90 in 2 separate assays. Associations between the RIA and the ELISA were higher, and the limits of agreement at 95% confidence intervals were narrower compared with those between the RIA and a modified ELISA procedure in which IGF binding protein complexes were extracted using HPLC. The samples were obtained from cows sampled over a period of 5 wk. These results demonstrated that the DSL-10-2800 nonextraction IGF-I ELISA was acceptably specific and sufficiently sensitive to be used to measure the extent and patterns of change in the plasma concentrations of IGF-I in samples from lactating Holstein cowsItem Variation in plasma concentrations of insulin-like growth factor-l in pasture-fed Holstein cows(Journal of Dairy Science 5(91): 1814-1821., 2008) Obese, F.Y.; Rabiee, A.R.; Macmillan, K.L.; Egan, A.R.; Humphrys, S.; Anderson, G.A.The objective of this 5-wk study was to determine dietary effects on plasma concentrations of insulin-like growth factor-l (IGF-I), as well as milk production and milk components in pasture-fed dairy cows. Thirty-two Holstein cows 4 to 5 wk postpartum were randomly assigned to 4 dietary subgroups. Feed was provided twice daily ad libitum at 0900 and 1600 h composed of fresh-cut pasture, meadow hay, and pelleted cereal grain to achieve differing levels of DMI and ME density (LL: 16.6 kg of DMI and 174 MJ of ME; HL: 17.3 kg of DMI and 181.1 MJ of ME; LH: 15.4 kg of DMI and 183.1 MJ of ME; HH: 17.9 kg of DMI and 213.3 MJ of ME with the first letter indicating DMI and the second ME, and with H indicating high and L indicating low, respectively). The first day cows were placed on their diets was designated d 0. Concentrations of IGF-I were measured in frozen-thawed samples of plasma using a verified ELISA. Dietary treatment had affected plasma concentrations of IGF-I by d 7 with cows on high ME diets having greater IGF-I concentrations at d 14 (83.7 vs. 45.6 ng/mL) than cows on the low ME diets. The level of DMI had less effect on plasma concentrations of IGF-I at d 14 (72.2 vs. 57.1 ng/mL). Dietary treatment effects on these concentrations had stabilized by d 21. Day-to-day variation in mean plasma concentrations of IGF-I within each dietary treatment was low during an intensive period of daily sampling for 14 d (from d 22 to 35). Within-cow day-to-day variation was also low compared with that among cows within the same dietary group and was associated with a high repeatability in the day-to-day concentration of IGF-I in individual cows. Intraclass correlation coefficients for IGF-I ranged from 0.56 (+ 0.14) to 0.88 (± 0.06) with a combined (pooled) value for the 4 subgroups of 0.77 (±0.05). The ME and DMI effects (H vs. L) at d 35 were 79.3 vs. 41.4 and 62.0 vs. 55.7 ng/mL, respectively. Although the ME and DMI differences also affected milk yield and compositional parameters, the effects were not as proportionately great as those measured for IGF-I. Altering the ME or DMI components of the pasture-based diets produced changes in plasma IGF-I concentrations that did not become stabilized for 3 wk, but were then highly repeatablefor individual cows within each dietary group. Both observations have relevance to interpreting data related to plasma concentrations of IGF-I in lactating Holstein cows.