"It was lying on its side, had lost its appetite and was breathing heavily," she told the Thomson Reuters Foundation from her farm in Meru, in eastern Kenya.
With her husband she decided to turn to WeFarm, a text-based network of small-scale farmers, for help.
Within an hour, their text – "one of my lactating cows cannot stand" – generated a flurry of suggestions, from "feed your cow with minerals rich in calcium" to "make sure the cow shed is clean and well-drained so the animals don't slip".
"I realized our cow had milk fever, so gave it calcium-rich feed and it was standing again within hours," Kagendo explained.
She is one of many Kenyan small-scale farmers who lack good information – mostly due to a lack of internet access – on how to manage problems from dry spells to diseases, local farm experts say.
As a result, such farmers often lose their harvest or animals, they said.
But WeFarm, a farmers' network launched in Kenya in 2014 and more recently expanded to Uganda and Peru, allows people to ask a question by text message and receive advice from their peers.
The service, whose Scottish co-founder Kenny Ewan describes it as "the internet for people with no internet", is free to use and only requires a mobile phone.
Farmers text questions to a local number, and WeFarm transmits the message to users with similar interests in the area, tapping into their knowledge.
"We want farmers to get answers to their problems without needing to access the internet, so the information is available to all," said Mwinyi Bwika, head of marketing at WeFarm.
Although the platform also exists online, over 95 percent of users choose to use it offline, he said.
Information gap
Kagendo's said that when her animals were ill or her maize crops too dry, she used to have to hire an extension officer to help solve the problem.
"But we had to pay a fee ranging from 500 to 2,000 Kenyan shillings ($5-20) and most of the time the officer didn't even explain their diagnosis," she said.
That cut into her family's income and left them no better able to understand the diseases facing their cattle and their crops.
"We cannot even afford a smart phone to go online, so finding credible information was near impossible," she said.
According to Bwika, small-scale farmers often lack the information they need because of a lack of cash - most live on less than a dollar a day – as well as poor internet connection and low literacy levels.
"Ewan realized that farmers living just a few miles from each other were facing the same challenges, but with no way to communicate about them. So he created a platform to connect them," Bwika said.
Joseph Kinyua, another farmer from Meru who grows vegetables, said he spends at least 30 minutes per day using WeFarm.
"It's taught me anything from using pest control traps to ensuring that my sprinklers don't put out too much water," he said. "And I know the methods are proven and tested by other farmers."
The knowledge has helped improve the quality of the kale he grows, he said, enough that "I can now sell a kilo at the market at 70 shillings ($0.70) compared to 50 ($0.50) previously".
Preventing problems
While the platform might receive dozens of replies to a question, it only sends out to the user a selection of answers judged correct, Bwika said.
But it uses the questions and advice received to help track disease outbreaks or extreme weather spells, and shares those insights with governments and non-governmental organizations, Bwika said.
"In doing so we hope to prevent disease outbreaks and track problems before they occur," he said.
Not everyone shares this optimism, however.
Mary Nkatha, a farmer from Meru, said she found it hard to implement some of the recommendations she received from WeFarm without the practical guidance of an expert.
"If I am told to inject my cow with something, how do I make sure I do it in the right place? And where do I find the equipment?" she asked.
Fredrick Ochido, a Kenya-based consultant on dairy farming, also worries that the platform may be entrenching farmers' poor use of technology, rather than helping them keep up with new trends.
The WeFarm platform has over 100,000 current users in Kenya, Uganda and Peru, and its operators hopes to reach one million farmers in the next year. They also aim to expand the effort to other countries, including Tanzania.