Sow hemoglobin: Potential biomarker for identifying ‘at risk’ sowsSow hemoglobin: Potential biomarker for identifying ‘at risk’ sows
Anemic sows experience prolonged farrowing durations, requiring more assistance with piglet delivery.
July 18, 2024
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By Katlyn McClellan and Eric Weaver, South Dakota State University
When you think of iron status, what is the first thing that comes to mind? Maybe iron for newborn pigs? Or, “Iron sharpens iron?” Maybe iron as a symbol of strength? This article is focused on the latter point in sows.
The swine industry's pursuit of genetic advancements to enhance reproductive efficiency has yielded success, but it has also led to a concerning increase in sow mortality and removal rates. The long-term profitability of swine farms hinges significantly on the maintenance of a healthy sow population. A current goal of our program at SDSU is the early identification of at-risk sows to proactively address nutritional status and complications that could result in negative outcomes.
One concern is the emergence of sow anemia as a significant issue with potential adverse effects. Recent studies in sows indicate variable degrees of anemia at different stages of pregnancy or lactation with a greater prevalence of anemia in older parity sows. Despite industry levels of iron into sow diets being several times higher than the published recommendations, deficiencies of iron may still arise due to escalating iron demands associated with larger litter sizes resulting from prolific breeding. Supplementing with additional dietary iron may not necessarily improve or eliminate anemia which may suggest that the cause of it is related to iron metabolism and losses rather than dietary iron supply.
Good runners can run a marathon faster than the time it takes sows to farrow 18-20 pigs. Limited understanding exists regarding the implications of anemia in sows. Early human epidemiology studies have linked anemia to conditions such as dystrophic dystocia or prolonged labor. It is plausible to assume that similar implications could affect an anemic sow due to physiological similarities.
Anemic sows are expected to have reduced oxygen transport capability, potentially leading to inadequate oxygen supply during farrowing, thereby contributing to a prolonged farrowing duration. Increased farrowing duration has been linked to a higher incidence of stillbirths, primarily attributed to the prolonged process leading to hypoxia in piglets. Furthermore, extended farrowing durations expose sows to heightened stress levels, increased inflammation, and a greater risk of retained pigs and post-farrowing infections.
Research conducted at South Dakota State University has shed light on the potential implications of anemia during the farrowing process. The study evaluated the impact of hemoglobin concentration, a reliable indicator of anemia, on the farrowing duration in sows. A total of 101 female pigs of PIC genetics were tested for HbC on day 112 of gestation and on day 2 of lactation. The sows ranged from parity 0 (gilts) to parity 3, with sample sizes of 16, 15, 24 and 46 for parity 0, 1, 2 and 3, respectively. Sows were classified as either 'anemic' or 'non-anemic' using a threshold of 10 g/dL based on previous research associating HbC below this threshold with increased stillbirth incidence.
HbC testing was performed using a rapid handheld device (HemoCue 201+ Hb analyzer). This device requires only a small drop of blood from the ear vein and provides results in less than 60 seconds. The method is relatively non-invasive, and compared to laboratory testing, it is cost effective. Introducing HbC testing on sow farms with such efficient tools could be both practical and beneficial for producers. If HbC testing is not feasible for a farm, recognizing clinical symptoms of anemia in sows becomes crucial. Anemic sows may exhibit lethargy, sluggishness and a lack of energy. Consulting with a veterinarian to understand the key symptoms of anemia in sows and educating barn staff on these clinical symptoms are essential steps.
To monitor the farrowing process, surveillance cameras were employed, complemented by human observation (checked hourly by trained research technicians and barn staff). Sleeving, following barn protocol (using obstetrical sleeves and lubricant, ensuring not to touch crate surfaces with gloved hands prior to sleeving), was employed when 60 minutes had passed since the birth of the previous piglet. Oxytocin was not administered during this experiment.
Farrowing duration was defined as the interval of time elapsed between the birth of the first and last piglet of the litter. The actual birth time for each piglet born was recorded. Identification of stillborn piglets was done using a lung flotation technique. Individual piglet weight and sex was recorded within 18h after farrowing. Farrowing duration was categorized as either prolonged (> 300 min) or efficient (≤ 300 min). All instances of sow removals were tracked from the point of farrowing through the subsequent reproductive cycle until the conclusion of their pregnancy, and were categorized as 'stay,' 'removed,' or 'dead.'
Hemoglobin testing at day 112 categorized 53 sows as anemic (< 10 g/dL) and 48 as non-anemic (≥ 10 g/dL). Farrowing duration was longer (P < 0.001) in the anemic sow group than in the non-anemic sow group (Table 1), with no difference observed in total born between the two groups. Additionally, there were no significant differences in piglet birth weight or total litter weight between anemic and non-anemic sows. Stillborn rates did not differ between anemic and non-anemic sows, however, a weak negative correlation (r = -0.20; P = 0.045) was observed between sow HbC at day 112 of gestation and stillborn rates.
When examining the sow HbC data more precisely (Table 2), sows were categorized as 1, 2, 3 or 4 for HbC ranges of < 9.0, 9.0 to 9.9, 10.0 to 10.9 and ≥11 HbC, respectively. Category 1 sows had a greater (P = 0.001) farrowing duration than all other HbC categories. Category 2 sows had a greater farrowing duration than category 3 (P < 0.001) and 4 (P < 0.001). Categories 3 and 4 sows had farrowing durations that did not differ; however, both were higher (P < 0.001) than categories 1 and 2. This indicates that as HbC levels decrease, farrowing duration increases.
Based on anecdotal evidence from this study, 41% of the sows entering farrowing in an anemic state either died (n = 5) or were removed (n = 19). In contrast, 22% of non-anemic sows died (n = 1) or were removed (n = 10). When examining sows removed based on farrowing duration, 41% of those with prolonged farrowing (> 300 minutes) died (n = 5) or were removed (n = 22), whereas sows with efficient farrowing (≤ 300 minutes) experienced a mortality or removal rate of 14.3% (n = 1 died, n = 4 removed).
Despite similar reproductive parameters such as total born, average piglet birth weight and total born weight between anemic and non-anemic sow groups, anemic sows (< 10 g/dL HbC) endured farrowing durations twice as long as non-anemic sows (≥ 10 g/dL HbC). This prolonged farrowing duration may be attributed to physiological responses associated with anemia, such as reduced muscle strength and uterine contractions, similar to observations in anemic human subjects during labor.
Bottom line: Iron status appears to be a risk factor affecting the health of prolific sows. Based on our observations, anemic sows experience prolonged farrowing durations, requiring more assistance with piglet delivery, whereas non-anemic sows have quicker and less problematic farrowing events, often requiring minimal to no assistance. Strategies to manage iron status need to be developed.
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