Variation in plasma concentrations of insulin-like growth factor-I in pasture-fed Holstein cows.

The objective of this 5-wk study was to determine dietary effects on plasma concentrations of insulin-like growth factor-I (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 repeatable for individual cows within each dietary group. Both observations have relevance to interpreting data related to plasma concentrations of IGF-I in lactating Holstein cows.

Measuring concentrations of insulin-like growth factor-I with an enzyme-linked immunosorbent antibody assay in plasma samples from Holstein cows.

This study describes the use of a commercial nonextraction ELISA to quantify total concentrations of insulin-like growth factor-I (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 cows.

Preliminary trials using abate to control Kabowra flies in the Rupununi, Guyana - abstract

Control of Simulium (called Kabowras in Guyana) black flies is usually directed to the larvae which breed in fast flowing waters. The purpose of the project was to determine the effectiveness of Abate Insecticide 200E in controlling Simulium sp., in a selected river in the Rupununi Savannah, Guyana. Two bioassays were carried out on the San Jose River near Lethem, Rupununi to determine the effective distance of Abate 200E at a concentration of 0.3 ppm during August, 1979 along a 2.4 km and 3.5 km stretch of the river. River discharge rates were calculated at a point of injection of the Abate. The volume of Abate required to give a concentration of 0.3 ppm when dispensed over approximatelty thirty minutes at the measured discharge was dripped into the stream. Counts of larvae on marked vegetation were made at several points before injection of Abate and four and nineteen hours after injection. The results of the first bioassay over 2.4 km showed at 57.8 percent drop in larvae four hours after injection of larvicide and a 99.3 percent drop within nineteen hours. Larval mortality was 97 percent at 2.4 km. Larval counts after the second Abate application two weeks later at 3.5 km showed a 52.8 percent drop after four hours and 96.1 percent after nineteen hours. Larval mortality was 100 percent at 2.7 km and 9.3 percent at 3.5 km. Larval counts were very low during the subsequent four weeks. Abate 200E at a concentration of 0.3 ppn was found to be effective in killing Simulium larvae over a distance of 3.5 km with a mortality of 93 percent nineteen hours after injection of larvicide. These trials should continue using lower concentrations of the larvicide (AU)

The black fly (simulium) problem in the Rupununi Savannahs, Guyana - abstract

Simulium black flies (called Kabowras in Guyana) are not known to carry diseases in Guyana, but they become a serious nuisance at certain times of the year in the Rupununi Savannahs. The present project was designed to study the bionomics of the nuisance species. Of about 20 species of black flies known from Guyana, 2 are serious manbiters; Simulium incrustatum and S. sanguineum s.l. The former appears in large numbers near small creeks and rivers, while the latter seems to be associated with larger rivers such as the Takutu and Rupununi. Peak densities of the two species appear at the height of the rainy season, but drop rapidly at the onset of the dry season. A peak biting rate of 928 flies per man hour was recorded for S. incrustatum and 764 flies per man hour for S. sanguineum s.l. Data obtained so far indicate that the two species tend to stay near river banks rather than the open savannahs. Both species are diurnal; none were collected after dark. For S. incrustatum there are early morning and late afternoon peaks. S. sanguineum s.l. peaks towards mid-morning and declines in the afternoon. The diurnal activities can be affected by rainfall and cloudy conditions. S. incrustatum shows no marked preference for humans or animals, but S. sanguineum s.l. shows a marked preference for livestock, dividing its attention almost equally between a cow and a horse during a comparative study. Because of their high biting rates these flies are serious pests, sufficient to discourage people from settling and developing the area. Further, their attacks on cattle may cause severe blood loss, annoyance and subsequent loss of weight resulting in financial loss to farmers (AU)