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March 26, 2017

By: Kim Gleason1, PhD, Lynn Edens2, and Arturo Pena2

Can a Cria’s Immunity Be Predicted By the Dam’s IgG Before Birth?

 

Can a Cria’s Immunity Be Predicted By the Dam’s IgG Before Birth?
Kim Gleason1, PhD, Lynn Edens2, and Arturo Pena2
1 Dancing Horse Farm, Pemberton, NJ; 2Little Creek Farm, North Salem, NY

That is one question that Kim Gleason and Lynn Edens asked over a year ago when they began a multi-faceted, multi-site research study. One of the goals of their massive research project was to determine if an IgG sample taken from females within 60 days of anticipated birth could predict failure of passive transfer. Cria are born without a functional immune system and rely on immunity passed from mom in the form of IgG at birth through colostrum. In a normal healthy dam at birth, a large bolus of immunity is passed into her colostrum that is ingested by the cria as soon as it stands and begins to suckle. Because of mechanics within the rumen of a neonate, the highest rate of IgG absorption from colostrum into the cria’s bloodstream occurs within a few hours of birth. By 24 hours after birth, that absorption declines to nearly zero percent. That is why it is so important that a newborn cria is able to stand and nurse its mom within a few hours of birth-to get the most immunity when they can absorb it at the maximal efficiency. Failure to obtain these necessary immunoglobulins at birth results in a condition referred to as Failure of Passive Transfer (FPT), and is the leading cause of neonatal mortality in alpacas. It is estimated that approximately 1 in 4 (25%) of all cria born in the U.S. have some form of FPT.
There are many circumstances that contribute to FPT, both from the cria’s perspective and from the dam’s perspective. Cria that are born prematurely, cold, or weak or after a difficult birth (dystocia) are at risk of not being able to stand and suckle their mom’s rich colostrum within a few hours. Also, cria that are born with retracted or contracted tendons, or weakness in the stifle/hip may have difficulty standing to nurse, or even demonstrate a complete inability to stand at all. All of these visually obvious situations would be considered critical situations and would require immediate managerial intervention in the form of supplemental colostrum or even costly hospitalization with such risky procedures as plasma transfer. Left unattended to, these cria could easily succumb to life threatening septicemia and weakness. Besides physical impairments, there are also physiologic problems within the cria that may prevent proper absorption of IgG from the colostrum, even though it is able to immediately stand and nurse.
From the dam’s perspective, there are numerous factors as well that may contribute to FPT. Dystocia, no or low colostrum, maiden rejection of cria that is quite common in alpacas, or failure to transfer IgG into her own colostrum. It is this area that the authors set out to study and to determine if it is possible to test the dam and predict FPT in the impending birth, and thus be pro-active with therapeutic and managerial intervention to possibly prevent costly and traumatic hospitalizations often resulting in cria mortality. In addition, the authors sought to determine if the dam’s IgG level would in any way predict weight gains and growth curves of subsequent cria.
For this prospective observational study, blood samples were taken from dams within 60 days of impending birth, and from cria within 36 hours of birth. Cria weights were recorded at birth, and at 2 weeks and 2 months. All blood samples were prepared at Little Creek Farm, where serum was extracted and analyzed on a commercial spectrophotometry analyzer for IgG level. Sixty total dam/cria birth pairs from both study locations were included in the study over a period of 1 year. Births occurred in all 4 seasons. Based on initial prepartum IgG levels recorded for dams, they were divided into 3 distinct groups: 1000-1499 mg/dl, 1500-2000 mg/dl, and IgG >2000 mg/dl. All data were analyzed by Analysis of Variance statistical methods.
A couple of interesting results came from this study so far. First of all, it can be reported that in this study, there was not a correlation between dam’s prebirth IgG and subsequent cria birthweights or growth curves. So the dams IgG level does not appear to be a predictor for slow or fast gaining cria. However, when considering the dam’s prepartum IgG level relative to her own cria’s IgG level, there was significant findings. Specifically, when the dam’s IgG level was in the range of the lower and mid-level group, cria were born with “normal” IgG levels by industry standards. However, when the dam’s IgG prebirth was > 2000 mg/dl, there were significantly more cria born with FPT. This is such an important finding and possible prebirth indicator for FPT in alpacas, that the authors wrote a scientific paper that was recently accepted for publication in the prestigious veterinary scientific journal, Theriogenology. Results of this study were also presented to the veterinary scientific community at the national conference of Theriogenologists in Asheville, North Carolina this past July.
For a possible explanation as to why a higher IgG level in dams might result in FPT in cria, it was necessary to search through previous veterinary research studies conducted in other livestock species. Several studies were discovered in cows that linked heat stress to higher blood IgG levels and thus lower concentrations of IgG in colostrum. It was suggested that when a cow is severely heat stressed, there becomes a biological shunt that diverts IgG away from the udder for some reason, and then results in higher circulating levels of IgG. Additional studies in cows also reported that heat-stressed calves had a lower ability to absorb IgG into their systems, so that heat stressed calves developed FPT at a rate of 25%. The results of the present study in alpacas is consistent with the previous reports in cattle. A deeper analysis of the dams with prebirth IgG >2000 mg/dl revealed significantly more births in spring months. Since herd practices in the northeastern US states typically concentrate breeding efforts in spring months, AND, typically alpacas are not shorn until mid to late spring, typically alpacas could be birthing in nearly 365 days of fiber growth. With these considerations, it is not inconceivable that many prepartal dams, at least in the northeast, have some degree of heat stress prior to birth, therefore providing further validation for these current study results. More births with FPT occurred in the spring months and to dams that demonstrated an elevated prebirth IgG level.
These preliminary results suggest that it may indeed be possible to use a dam’s blood IgG level before birth as a predictor for potential problems in the cria. Even if the cria presents normally and stands and nurses within a couple of hours, FPT is still possible if the quality of the mother’s colostrum is compromised. This is a finding that is not as obvious as contracted tendons or inability to stand, which makes this so concerning. In these type of situations, FPT may go unnoticed until a day or 2 after birth when the cria isn’t gaining weight properly and by then it is past the window of optimal absorption and the owner finds themselves in a veterinary emergency room in the middle of the night. Hopefully the results of this study will get breeders thinking about some alternative management practices, like prepartum testing a dam, that are inexpensive and that could save a cria and costly interventions, by anticipating FPT prior to birth and being proactive with supplemental colostrum right out of the gate. The authors are currently investigating the role of heat stress on passive transfer in alpacas and hope to share their findings with both the scientific and breeder communities in the near future.