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Biomedical subjects

G E Shook

Publications and source records attributed to G E Shook.

25 records · Page 2Linked to original sources
PubMed1989

Genetic and economic responses to breeding programs that consider mastitis.

Eight breeding programs were evaluated with a simulation study using discounted gene flow. Discounted economic responses and annual genetic changes were calculated. The evaluation was over 25 periods of 13 mo and the population modeled was DHI cows served by AI sires in the US. A breeding program without regard for mastitis gave annual genetic increases of 53.5 kg milk, 2.24 kg fat, .020 cases of mastitis, and an economic response of $98.24. Including SCC or mastitis in selection indexes that maximize economic gain reduced the rate of improvement in yield traits by 1 to 2% but did not reduce clinical mastitis. Instead these indexes slowed the rate of increase in clinical mastitis by 20 to 25% and increased response in economic merit by less than 1%. Restricted selection, which permitted no genetic change in mastitis, reduced the rates of improvement by up to 27% for yield and 17% for economic response. Direct selection against mastitis is unrealistic due to lack of field data on clinical mastitis. Indirect selection would be less efficient than predicted here, due in part to incomplete enrollment in SCC testing program. Simultaneous improvement of both yield and mastitis apparently is not economically desirable due to the antagonistic genetic correlation between yield and mastitis and to the relatively greater economic value and higher heritability of yield.

Analysis of Variance↗
PubMed1987

[Milk cell count as a selection criterion in breeding dairy cattle with improved resistance to mastitis].

The cell counts in the milk of female progeny of thirty-one bulls of the Meuse-Rhine-IJssel breed were determined in three breeding areas in the Netherlands, viz., in the provinces of Overijssel, Gelderland and North Brabant. The individual cell counts of the milk of 1,741 females in their first lactations were determined in study I. Eleven bulls, the female progeny of which showed high or low average cell counts in the milk, were selected on the basis of these results. The quarter milk of older females sired by these eleven bulls was studied (bacteriological examination and determination of cell counts). Females in their first and second lactations were examined in study II. This was done in 1,071 females sired by ten of the initially selected eleven bulls. The heritability of the cell counts in the milk of the females sired by thirty-one bulls, which cows were in their first lactations, was 0.081. On the basis of geometric means of the cell counts in the milk of the females in their first lactations, the rank order of the bulls which had sired them corresponded inadequately with that of half-sibs in their third and fourth lactations. In study II, the similarity in rank order of these two age groups was much better: groups of female progeny averaging low cell counts and percentages in their first lactations corresponded with low cell count averages and percentages of quarters of older half-sib progeny in their third and fourth lactations, which quarters were found to be positive on bacteriological examination. There were some differences in rank order.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Sperm in poor quality semen from bulls during heat stress have a lower affinity for binding hydrogen-3 heparin.

Binding assays with [3H] heparin were performed using spermatozoa collected prior to, during, and following summer heat stress to dairy bulls. Ejaculates collected in August 1983 after a period of ambient temperatures exceeding 29.4 degrees C exhibited a high frequency of abnormal sperm, and motility was reduced in some samples. Sperm in samples collected during heat stress possessed dissociation constants for binding [3H] heparin ranging from 134.5 to 163.2 nmol. In contrast, sperm in semen collected prior to and after heat stress had significantly lower dissociation constants (higher affinity) for [3H] heparin, 12.9 to 56.4 nmol. The number of binding sites for [3H] heparin on sperm did not change among collection periods. It was concluded that the binding affinity for [3H] heparin may reflect membrane integrity of bull sperm.

Animals↗
PubMed1987

A lactation measure of somatic cell count.

Adjustments and weights to combine individual sample day SCC into a lactation measure were developed from 182,446 Holstein lactation records completed in 1984 from herds primarily in the western United States. Data included 1,660,782 sample day SCC expressed as log base 2 scores. Stage of lactation effects were investigated within average lactation score. Curves for lactations with averages less than 3.5 were essentially identical, which indicated that effect of stage of lactation did not increase with average somatic cell score. Lactations with averages above 4.5 did not display the typical curve of an early minimum followed by a gradual increase and, therefore, were excluded from estimating effects of stage of lactation and season. Curve for lactations with an average somatic cell score of 4.0 was intermediate. Small season effects were detected; scores were lowest in February and March and highest in August, September, and October. Parties after first had similar curves for effect of stage of lactation, but first parity showed relatively little increase in late lactation. Weightings were developed to combine adjusted sample day scores into a lactation measure. Weights were squares of correlations (computed from sample days grouped by month) between adjusted score for a given sample day and average of adjusted scores from other sample days. Weights were lowest at start of lactation, highest in midlactation, and intermediate at end of lactation.

Animals↗
PubMed1985

Factors related to milk loss in quarters with low somatic cell counts.

Relationship between milk production and milk composition was studied through comparisons of udder halves within cow. Cows were milked by milking unit for separate quarters of udder. Six trials had six cows per trial. Trial length was 3 d, and milkings were at 12-h intervals. Foremilk samples were taken aseptically for bacterial analysis. Milk weights by quarter were recorded, and samples by quarter were analyzed for concentrations of lactose, somatic cells, and chloride. Milk cell differential counts and N-acetyl-B-D-glucosaminidase activity also were determined. Eighty-four percent of quarter milk samples contained less than 400,000 cells/ml. Differences between right and left udder halves with respect to all measurements were computed. For halves of udders within-cow correlation coefficients for differences between production and log(base 2) somatic cell count, lactose, chloride, bacterial presence, neutrophil percent, lymphocyte percent, macrophage percent, and N-acetyl-B-D-glucosaminidase activity were -.16, .23, -.31, .09, .12, .01, -.14, and -.41. Regression coefficients of milk production (kg) on somatic cell count log(base 2) cells per milliliter, lactose (%), chloride (mg/100 ml), and N-acetyl-B-D-glucosaminidase (nmol/min per ml) were -.12, .57, -.05, and -.46. From negative correlations between production and concentrations of chloride, somatic cells, and N-acetyl-B-D-glucosaminidase activity, differences between udder halves in production may be related to changes of the blood-milk barrier, leukocyte diapedesis, and loss of integrity of secretory cells.

Acetylglucosaminidase↗
PubMed1985

Effect of bull selection for somatic cell count in first lactation on cell counts and pathogens in later lactations.

Somatic cell counts were measured one time on Meuse-Rhine-Ijssel cattle in The Netherlands. Experiment 1 involved 1,741 first lactation daughters of 31 bulls. Eleven bulls with daughters with either high or low average cell count were selected for further study of their daughters in third and fourth lactation. Cell counts and bacteriological tests were performed on 684 of the older daughters. A second experiment was conducted to measure daughters in second lactation and to obtain additional daughters in first lactation. This experiment recorded cell counts of 1,071 daughters of 10 of the bulls selected in Experiment 1. Heritability of the natural logarithm of cell count in first lactation was .081 based on daughters of 31 bulls in Experiment 1. Geometric daughter averages ranged from 206 to 700 X 10(3) cells/ml. Transmitting ability of bulls was estimated by the regressed least squares method. Ranking of bulls on first lactation cell count was different between the two experiments. Management factors and stage of lactation effects could be responsible for these differences. Within Experiment 2, the ranking of bulls on cell counts was nearly identical between first and second lactation. Daughter groups with low average cell count in first lactation in Experiment 2 had low averages in third and fourth lactation although some changes in ranking did occur. These results are consistent with a low to moderate genetic correlation between lactations for cell count. In general, daughter groups with higher average cell count had higher percentage of quarters with mastitis pathogens.

Animals↗