Heat stress affects all aspects of dairy productivity; and producers and researchers alike constantly seek ways of mitigating the impact of high temperatures and humidity on performance, reproduction and general health. Nutritional factors ranging from diet physical characteristics to nutrient content and form interact with the cow’s response to environmental conditions, and it has been suggested that a recently FDA-reviewed form of selenium (Sel-Plex®, Alltech® Inc.) might be better able to meet demand for this critical nutrient, especially under stressful circumstances.
Selenium is essential for fertility in cows as well as other species. Although the mechanism is not understood, it is well-know that selenium deficiency is a factor in the incidence of retained placenta. Forages and crops grown in the southeastern US are well-known to be naturally low in selenium; and as a consequence producers have until recently had to rely on inorganic selenium sources (sodium selenate, sodium selenite) added to the diet. While these sources prevent abject deficiencies, rumen microbes reduce much of ingested inorganic selenium to a less absorbable form. Because of this, injections of inorganic selenium are often used pre-partum and/or postpartum to help meet selenium demands of the periparturient cow. Injected inorganic selenium bypasses the problem of rumen reduction, but because it is in a form that cannot be stored, any inorganic selenium that cannot be readily used in selenoprotein production is rapidly excreted. In contrast, yeast, like plants, convert selenium to selenoamino acids, particularly selenomethionine. This form is not destroyed by rumen microbes and in contrast to selenite, cattle can store selenoamino acids for periods of greater need.
This experiment investigated effects of selenium form in a Florida herd that followed two different reproductive management programs to examine dietary effects on pregnancy rate. The experiment was conducted during the mid-May to September heat stress period. During this time the average temperature-humidity index between noon and 3:00 p.m. exceeds 72o. A comparable experiment was conducted in California under the supervision of Dr. Jose E-P. Santos of the Veterinary Medicine Teaching and Research Center, University of California -Davis, Tulare, CA.
Methods
The trial involved 574 pre-parturient multiparous and primiparous cows with body condition score (BCS) greater than or equal to 2.75 (scale 1 – 5). Cows that had dystocia requiring veterinary assistance, caesarian section, or fetotomy were excluded, as were cows with gestation lengths less than 265 days. Median BCS at enrollment did not differ between groups and was 3.0.
The experiment had a 2 x 2 factorial design consisting of two dietary treatments and two reproductive management programs. Cows were assigned (-23 ± 8 days postpartum (pp)) to receive dietary selenium either as selenium yeast (Sel-Plex, Alltech; n=289) or sodium Se [SS; n=285]) at 0.3 ppm in dry matter for >81 d. Cows within each dietary treatment were assigned randomly to one of two reproductive management programs (Presynch-Ovsynch vs CIDR-Ovsynch [i.e., Ovsynch begins 3 d after withdrawal of a 7-d-CIDR]). Rectal temperature was recorded in the morning for 10 dpp. Vaginoscopies were at 5 and 10 dpp to determine uterine health. All cows were resynchronized for a second service with Ovsynch at 20-23d after first service and pregnancy diagnosis at 27-30 d after first timed artificial insemination (TAI). Cows in estrus after the first TAIwere artificially inseminated up to the second TAI service. Strategic blood sampling determined anovulatory status at Ovsynch and ovulatory response after TAI to first service. Pregnancy rate (PR) at second service was determined by rectal palpation at ~42 dpp. Blood was sampled for Se (n=20 cows/diet) at -25, 0, 7, 14, 21 and 37 dpp.
On a subset of 40 cows, samples were collected for immune status measurements. Innate immunity was determined by phagocytic and oxidative burst capacity of neutrophils in whole blood using a dual color flow cytometric method. Samples were collected at -26, 0, 7, 14, 21 and 37 dpp for neutrophil function and for Se measurements in plasma. Adaptive immunity was monitored with anti-IgG to Ovalbumin (Ovalb) after vaccination with Ovalb antigen (1 mg [i.m.]) dissolved in an E. coli J5 endotoxemia preventivevaccine at -60 and -22 ± 6 dpp (day of initiating SS [n=47] and SY [n=38] diets) and again at parturition (day 0) with Ovalb dissolved in PBS with Quil-A adjuvant. Serum samples were collected on days of immunization and at 21 and 42 dpp. Anti-IgG to Ovalb was measured via an ELISA assay with absorbance (OD) read at 405 and 650 nm.
Results
There were no detectable differences between reproductive management programs of Presynch-Ovsynch vs CIDR-Ovsynch on pregnancy rates and ovulation responses, thus only responses to selenium form are presented here.
Effects of organoselenium on reproduction and milk production
Organic selenium improved the second service pregnancy rate (Sel-Plex 17% (34/199) vs sodium selenite 11.3% (24/211), P<.05) (Figure 2), although no effects on first service PG at ~d30 or pregnancy losses between ~d30 and ~d42 were noted.
Feeding Sel-Plex improved uterine health status within 10 days postpartum, as indicated by vaginoscopy (at 5 and 10 dpp) for clear (47.1% [217/460] vs 35.0% [153/437]), mucopurulent (43.4% [200/460] vs 47.8% [209/437]) and purulent (9.3% [43/460] vs 17.1% [75/437]) discharge scores for Sel-Plex and sodium selenite cows, respectively (P<.05).
Milk somatic cells (291,618 cells/mL), and frequencies of retained fetal membrane (9.7%), mastitis (14.4%), anovulation (17.7%) and synchronized ovulation after TAI (82.5%) were unaffected by diets or reproductive programs.
Sel-Plex-fed cows produced more milk in the summer months than did cows fed sodium selenite as noted in the California trial (Figure 1).
Effects of organoselenium on innate and adaptive immunity
Feeding Sel-Plex increased plasma Se concentrations compared with feeding sodium selenite (.087>.069 ± .004 ìg/mL; P<.01) (Figure 3).
Phagocytosis and killing activity of neutrophils from whole blood were increased chronically in primiparous cows and acutely in multiparous cows in the postpartum period (Figure 4). Percentage of gated neutrophils that phagocytized E. coli and underwent oxidative burst did not differ between diet groups at -26 dpp (44.6 ± 4.6%). For subsequent samples, a diet*parity*day interaction was detected (P<0.05): Sel-Plex improved neutrophil function at parturition in multiparous cows (42 ± 6.14% > 24.3 ± 7.2%) and at 7, 14 and 37 dpp in primiparous cows (53.9 > 30.7, 58.6 > 41.9, 53.4 > 34.8%, respectively; pooled SE=6.8%).
Anti-immunoglobulin response to immunization with ovalbumin was greater in multiparous cows fed Se-Plex at 21 and 42 dpp (1.91 ± 0.1 > 1.24 ± 0.07, 1.44 ± 0.7 > 0.99 ± 0.07 OD, respectively; P<0.01) (Figure 5), but not in primiparous cows (1.40 + 0.08 OD). Anti-IgG to Ovalb did not differ between diets at -60 and -22 dpp (0.18 ± 0.01 and 0.97 ± 0.04 OD).
Feeding Sel-Plex reduced occurrence of fever in multiparous, but not primiparous, cows during the 10-d post partum period. Sel-Plex lessened the frequency of >1 event of fever (rectal temperature > 39.5 °C, with Sel-Plex 13.3% (25/188) vs sodium selenite 25.5% (46/181), P<.05). Frequency of fever events was unaffected in the first parity (40.5%).
Summary
Feeding organic selenium as Sel-Plex beginning at 26 days prepartum, elevated plasma Se concentrations and increased neutrophil function at the time of parturition. Furthermore, immunoresponsiveness was increased in multiparous cows during early lactation. Sel-Plex induced increased immunocompetence at parturition, which is normally a period of suppressed immune activity, and therefore may benefit subsequent postpartum cow health. Sel-Plex organic selenium improved milk yield, uterine health, and second service pregnancy rate during the summer months.
Figures from the PPT file:
Monthly DHIA milk yield (Slide 6)
Second service pregnancy rates (Slide 5)
Plasma concentrations of Se (Slide 1)
Whole blood neutrophil phagocytosis and kill (primiparous) (Slide 2)
Serum Anti-Ovalbumin antibody (Slides 3-4)