Hi, my name is Caroline González-Vega, and I'm a third year Ph. D. student in Dr. Stein's lab. And today, I have the pleasure to talk about the digestible calcium requirements and calcium and phosphorus balance for weanling pigs. This is the outline of the presentation. First, I will start with a brief background about calcium requirements, and then I'll explain the two experiments that we conducted. The first experiment is a growth performance study, and the second experiment is a balance study. At the end, I'll give you some conclusions. We know that the requirements of calcium reported in the NRC 2012 are expressed as total calcium requirement. The reason that these values are still reported as total calcium requirement is because there were no data available for digestible calcium. This is an example of the requirement of phosphorus and calcium for an 11-25 kg pig. So, the requirement for phosphorus is expressed as standardized total tract digestible phosphorus, and is 0.33. The requirement for calcium is expressed as total calcium, and is 0.70. The NRC determined the total calcium requirement by multiplying the digestible phosphorus value by 2.15. During recent years, studies have been conducted to determine the digestibility of calcium. And it has been determined that there are endogenous losses of calcium. Therefore, we have to correct the apparent total tract digestibility values to obtain the standardized total tract digestibility values. The reason that we want to determine standardized total tract digestibility values is because these values are additive in mixed diets. Therefore, standardized total tract digestibility values of calcium for calcium supplements have been recently reported. Currently, we are formulating diets using total calcium and digestible phosphorus values. But we want to move to formulate diets using digestible calcium and digestible phosphorus. But first, we need to determine the digestible calcium requirement. Therefore, these two experiments were conducted to determine the requirement for digestible calcium by 11-25 kg pigs: the growth performance study and the balance study. It's important to mention that for these two experiments, the same batch of diets were used. And here in this slide, we can see six diets that contain the same amount of digestible phosphorus, that is represented in orange and is 0.36%. And in blue is represented the digestible calcium, and it ranged from 0.32 to 0.72%. These are the same six diets, but instead are expressed as total phosphorus and total calcium if you are more familiar with these values. And here, we have the ratios that range from 0.71:1 to 1.89:1. We had two additional diets: Diet 7 and Diet 8. And these two diets contained the same amount of digestible calcium as Diet 6. However, the digestible phosphorus is different. For Diet 7, it's 0.33, and for Diet 8, it's 0.40. And the reason that we had these two extra diets was to confirm that the amount of phosphorus that we had in the first six diets was accurate. This is the ingredient composition of the six diets. As you can see, we have the same amount of corn, soybean meal, lactose, and monocalcium phosphate for the six diets. However, the amount of calcium carbonate was increasing as we increased the level of digestible calcium in our diets, and calcium carbonate was included at the expense of cornstarch. For the first experiment, we used 256 growing pigs, with initial body weight 11.4 kg. And we had eight diets, with eight replicate pens per diet. For each pen, we had two barrows and two gilts. And at the end of the experiment, we euthanized one barrow per pen and the femurs were collected to determine the bone ash, bone calcium, and bone phosphorus. For Experiment 2, we had 80 growing barrows with initial body weight of 13.1 kg. And we had eight diets, with ten replicate pigs per diet. We also had total fecal and urine collections. For both experiments, the data were analyzed using the Proc Mixed of SAS. And diet was the fixed effect and block was the random effect. We also used CONTRAST statements for the linear and quadratic effects, and the Proc NLIN for the broken line and quadratic line. Now, let's move to the results for the first experiment. First, let me set up this slide. In the x axis, we have the standardized total tract digestible calcium, and the y axis we have the average daily gain in kg/day. From this slide, I want to point out three things. The first thing is that at levels greater than 0.56% digestible calcium, the average daily gain is negatively affected. And this is maybe due to the negative effect that has high levels of calcium on the digestibility of phosphorus. The second thing I want to point out is that, at lower levels of calcium, the average daily gain was not affected. And this may be because the pigs were able to pull out calcium from the bones to compensate the low levels of calcium, and because this study was conducted for short time, only one month, we couldn't see the negative effect on average daily gain that maybe we could see if this study was conducted for longer time. The third thing I want to point out is that we were not able to determine the requirement for digestible calcium to maximize the average daily gain with these results. This is the bone ash in grams. And here we can see that levels greater than 0.48% digestible calcium maximized the bone ash in the pigs. The same value was obtained for bone calcium in grams. However, to maximize bone phosphorus in grams, a minimum level of 0.56% was needed. Now let's move to the results for the second experiment. This is the absorbed calcium in g/day. And we can see that as we increase the digestible calcium in our diets, we increase the amount of calcium absorbed by the pig. Also, the amount of calcium excreted in the urine increased as we increased the digestible calcium in the diets. However, the amount of phosphorus excreted in the urine decreased as we increased the digestible calcium in the diet. And this is because to retain phosphorus, we need to have enough calcium in the diet. So if calcium is deficient, the pig is not able to retain all the phosphorus, and will excrete it in the urine. This is the calcium retention in g/day. And a minimum value of 0.52% digestible calcium is needed to maximize calcium retention in the pig. And to maximize phosphorus retention, a minimum value of 0.48% is needed. This is a summary of some of the breakpoints that I showed before. So for bone ash, bone calcium, and phosphorus retention, is 0.48, and for calcium retention is 0.52. This corresponds to a standardized total tract digestible calcium:phosphorus ratio of 1.33 and 1.44. We see in the literature the calcium:phosphorus ratio for the whole body of the pig is between 1.18 and 1.54. So this indicates that our digestible calcium and digestible phosphorus ratio requirements are within this range. So in conclusion, the standardized total tract digestible calcium requirements for 11-25 kg pigs to maximize bone ash, bone calcium, and bone phosphorus is between 0.48 and 0.56%. And to maximize calcium retention and phosphorus retention is between 0.48 and 0.52%. To maximize growth performance, it appears to be less than 0.43%; however, more research is needed to determine the digestible calcium requirement to maximize growth performance. With this, I want to thank you for your attention, and I invite you to look at our web site to find more information about this research and other related topics about monogastric nutrition. And thank you so much, and Like us on Facebook!