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Biomedical subjects

E E Swierstra

Publications and source records attributed to E E Swierstra.

15 recordsLinked to original sources
PubMed1987

Reproductive traits of ewe lambs representing eight genetic types born in winter, spring, summer and fall.

Crossbred ewe lambs of eight genetic types (Dorset X 3/4 Dorset, DD; Dorset X 3/4 Finn, DF; Finn X 3/4 Dorset, FD; Finn X 3/4 Finn, FF; Romanov X 3/4 Dorset, RD; Romanov X 3/4 Finn, RF; Romanov X Western, RW; and Western X Western, WW) were used to determine age and weight at conception, conception rate, ovulation rate, litter size and prenatal mortality. Each cross was represented in five different lamb crops born in winter, spring, summer and fall. High conception rates (greater than 88%) were obtained in all crops of ewe lambs, even in those born in June and exposed to rams the same year. Only Western ewe lambs born in June and exposed to rams in year of birth achieved low conception (59%). Ewe lambs born in October and missing the breeding season in the year of birth were more than 100 d older than ewe lambs born earlier in the calendar year and bred the same year. Prenatal mortalities varied widely (8 to 18%) among lamb crops, with management suspected to be a factor. Additive genetic effects in ovulation rate and litter size of the Romanov were similar to that of Finn. Romanov crosses (RF, RD, RW) conceived at the youngest age (226, 227, 231 d), demonstrating that Romanov is an early-maturing breed.

Animals↗
PubMed1985

Year-round breeding of crossbred Dorset or Finnish landrace ewes using a synthetic light regimen.

A group of crossbred Dorset or Finnish Landrace ewes maintained under a synthetic light regimen (Light Treatment, 4 mo long days - 16 h light, 4 mo short days - 8 h light) and exposed to rams every 8 mo (January 1, September 1, May 1) was compared for lamb production over a period of 4.5 yr with two other comparable groups under natural daylight conditions, one exposed to rams once a year in the fall (Control I) and the other every 8 mo (Control II). Conception rates across breed type of ewe were 92% for Control I, 66% for Control II and 83% for Light Treatment ewes. Conception rates for May breedings only were 16% in Control II and 88% in Light Treatment ewes. Prolificacies of crossbred Finn ewes were higher (P less than .05) than those in crossbred Dorset ewes of Control I (258 vs 193%), Control II (187 vs 165%) and Light Treatment (238 vs 163%). The annual production at lambing from the crossbred Finn and Dorset ewes in Control I was 251 and 206 lambs/100 ewes exposed to rams, respectively. Corresponding productions were 231 and 178 for Control II and 296 and 211 for Light Treatment ewes. Mortality of lambs from the crossbred Finn ewes (27%) was higher (P less than .01) than that from the crossbred Dorset ewes (12%). Annual attrition of the crossbred Dorset ewes in Control I, Control II and Light Treatment groups was 5.2, 5.4 and 5.4%, respectively. Corresponding percentages of the crossbred Finn ewes were 7.0, 8.8 and 11.2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1975

The relationship between dialy sperm production as determined by quantitative testicular histology and daily sperm output in the stallion.

The relationship between daily sperm productions (DSP) and daily sperm output (DSO) was determined in eleven stallions. The DSO was determined by collecting single ejaculates, with an artificial vagina, at 24-hr intervals. The stallions were killed 24 hr after the last collection and the DSP was determined by quantitative testicular histology. The mean DSP was 8-0 X 10(9) (S.E. +/- 0-4 X 10(9), and the mean DSO was 7-0 X 10(9) (S.E. +/- 0-4 X 10(9)). It was estimated that 87% of the spermatozoa produced by the testes were harvested. The correlation between DSP and DSO was 0-80 (P less than 0-01), and between DSP and testis weight was 0-77 (P less than 0-01).

Animals↗
PubMed1975

Spermatogenesis and duration of transit of spermatozoa through the excurrent ducts of stallions.

The cycle of the seminiferous epithelium was divided into eight stages on the basis of meiotic divisions, shape of the spermatid nuclei and location of the spermatids with elongated nuclei. Duration of this cycle was 12-2 days (S.E. +/- 0-1) as determined by [3H]thymidine injections and autoradiography. The life-span of primary spermatocytes was 19-0 days, secondary spermatocytes 0-7 days, spermatids with round nuclei 8-7 days, and spermatids with elongated nuclei 10-1 days. Labelled spermatozoa entered the caput epididymidis 35 days, and appeared in the ejaculate 39-9 days, after the isotope injection. The mean minimal time required for spermatozoa to pass through the excurrent ducts was 4-9 days. However, the average transit time was estimated to be between 8 and 11 days. Variation in the duration of the cycle between species is discussed.

Animals↗