We never found out the cause of death on these cows, however I took a shot in the dark and dewormed them with ivomec plus and I also used a product called valvazen from zoetis. Started using minerals daily as well and came up with my own schedule on vaccines for clostridium, derriengue and anthrax. Vigantol AD3E from Elanco and Multimin 90.
In regards to weight gains. Grass fed your anywhere between 1/2lb to maybe 1 1/2 lbs per day maybe a smidge more. Feedlot I've heard crazy numbers(to me it's crazy) but I don't know it's true, I've heard 3-4 1/2 lbs per day, most of the beef is select grade. Unless you buy imported beef from USA, Nicaragua or Argentina then you'll have access to prime. People down there for the most part eat their steaks very well done/charred and if you serve it rare or med they will tell you it's not cooked. I would say only a small amount of the population knows what great steak is. I do know that there are a few wagyu beef producers down there but I think they are still trying to aclimate the herd to the tropics or are crossing them with another breed.
I have thought of using Simmental or senepol to cross but I'm afraid to do so because I think our herd is too commercial I was always under the assumption you get a better cross when your using two animals that are pure blood or close to it.
My contact in Mexico that I bought Corriente cattle from for years, bought a LOT of Chianina, Chianinia X Brahma, and Chiania x Charbray bulls from me. He sold them in Guatemala, Honduras, Nicaragua, Costa Rica, and Columbia & Venezuela. Maybe other contries too, but these are the ones I remember him telling me about. He said the Chiania are just as heat insect, and parasite tolerant as Brahma, and the bulls can really cover a lot of ground seeking out cows. and have very strong libidos. And they throw a lot bigger calves than with the straight Brahma, Indu-Brasil, etc, bulls. I dunno...I never tried.....but he said it is easier to get cattle into those other countries from Mexico than straight from the US. But, I figure you'd know the best way to do it.
And no, you wouldn't have to have purebred cows to cross with say, a Simmental. You just want to make sure the Simm bulls are registered. You might want to think about Charolais instead of Simm, though, to keep that white coat going, due to the heat. The last 3 or 4 years before he was killed last summer, he told me he'd as soon take a Chininia x Charbray bull if I could find them, as he would a Chi x Bra.
Maybe you could try a Charolais or Chiania bull and see if it improved your calves's sizes? Or both? You wouldn't have to worry about how the Chiania would aclimate, and I would guess a Charolais would fare better than a red or black Simm.
The last 25 years or so, cowboy poker has been gaining popularity for rodeo specialty acts, and PBR holds bull fighter competions for the bull fighters. Both of these use Mexican Fighting Bulls in these events. Not every MFB is good enough to make it into the arenas in Mexico, and not every ABBI bull raised bucks well enough to be used in rodeo and PBR events. Bucking bulls are mostly LH x Brah crosses, and a lot of the crosses are with Charolais. George (Jorge) did a lot of business with stock contractors, trading fighting bulls for any white bucking bull he could find. And he sent all of them further south.
I was wondering if anyone uses implants on new born calves(one month old) ? What experiences have you had? what brands have better response? I'm mostly wondering if your weaning weights are heavier. Intentions are to only use them on the bull calf's. 
